I would try to talk to him & see why he’s acting like that. If he doesn’t really give an answer then I’d ask him what he wants to do. Pick something & we’ll go do it. I would set a specific day each week to do something he wants. Go to the park, get ice cream, something like that. Even if he doesn’t reciprocate it hug him kiss him tell him you love him
I’m in the same situation. My daughter is 7 days old and her sister will be 3 in April. I still try and keep our routine and give her attention and include her when attending to our newborn but there is distance which is killing me
I would try taking him out on a “date” for something fun just you and him. I did that with my oldest when I had my youngest. It worked really well for him. The one on one time is important and sometimes it needs to be away from home and away from the siblings. We still do this and they are now 14 and 8 and they love our dates
Probably resentful if you can leave baby baby with dad and take him out on a date for some one on one
Don’t be too pushy with him and let him work through his feelings. Have dad remind him that mommy loves him and is there to help him too.
Take him outside the house to do something fun without the baby.
Have him help with the baby. Help feed, bathe. My daughter was like this but she was 19 months old when her brother was born. We took her out without her brother and spent the day with her. We also had her involved in bathing and holding the bottle while we fed him. It helped a lot.
Awe I’m sorry it probably breaks your heart a lil. He will come around,just give him special time for just you and him.he was used to being your only baby he probably just feels a little left out. He will come around .congratulations on your new baby!
Take him out, like to a park, just the two of you.
He will definitely come around. He still loves you. 4 years old was around the age that my son switched from ‘mommy AND daddy’s boy’ to pretty much being all about his dad.
He just like you and the rest if the family experienced a huge change. Being he is only 4, he probably doesn’t understand how to express his feelings very well.
Give him a little time to adjust, it is OK for him to be feeling this way.
Try different ways to let him feel included in all the changes, let him be a big brother helper, spend alone time with him when you can, give him a special big brother celebration day.
Lastly, try to relax and not take his feelings personally, that will cause anxiety for everyone…lots of changes and it’s ok. Congratulations!
My daughter was 5 when i had her sister….she wanted her sister to sleep in the dryer……
because she’s too nosy 
. That age they’ve adjusted to being by themselves.
It’ll get better 
promise.
Hand the baby to the Dad when he gets home and try to spend time with him then.
Take him on a mommy son date make it about him. I have 6 and I always find a way to have a bond with each child and build their bond with sibling.
It’s a phase mommy
He is jealous the same happened when I had my daughter but it was over when she could interact with his sister a bit more
He is mad at you…he will come around…just keep loving him.
Just try involve him as much as he wants to be with the baby don’t force it 
He will come around, it’s normal for him to push back or resent a little. He will warm up again, like suggested above have one on one time with him if you are able, even in his room if you aren’t able to go out or make a movie night with just him. Depending if you pump, breastfeed or formula of course
Ask him to help with his sister.
He may have gotten scared of the baby. Well intentioned people saying things like “you’re the big boy now…”, “it’s your job to…”, “don’t bug mommy and the baby…”, it’s a lot of pressure suddenly on a kiddo that once had free, undiluted access to mom before. Try involving him. Try telling him how proud you are and how much you also miss alone time together. That you’re ready for snuggles whenever he is ready too. Be available. Ask him to come sit with you while you fold laundry and the baby is napping for example. Give him 10 minutes of undivided attention just for him, if at all possible.
He’s just adjusting now. He feels left out/put of place. All big siblings have this at some point.
Kids sometimes have a really hard time adjusting to a younger sibling. They’re jealous they’re not the center of attention. Keep doing what you’re doing. He’ll come around when he realizes that even with a new baby everything will be ok.
Give him time to adjust…on his time.
Ok so my son did the same and I thought if I made him spend time with me it would really make him hate me. My son is in his twenties now and he has grown up feeling second best. We are doing better now but I would give any for him not to have felt that way. I suggest praise him and lavish him with love and special treats just for him. He is feeling like you love baby more because baby requires your care but he doesn’t understand that. Also maybe as long as baby is safe let baby cry a little to finish up something with him, because he is so important too. 4 is not to young to start asking him how he feels and why he doesn’t want to do anything with you. And that it makes you sad because you love him and want to have fun like you used to. If that fails call a therapist. Emotional health is part of physical health. Praying for you momma 
He feels you have replaced him
I went through the same thing with my oldest after I had his brother. He used to sit with me in the recliner everyday for hours just hanging out. After I had my youngest he would refuse and it started immediately after I brought baby home from the hospital. I think at that age they just already know baby needs mom’s attention more. My oldest was a huge mommas boy and my partner in crime for everything but after baby he just started wanting to hang out with dad all the time. Now that they are both a couple years older it’s gotten better and he will come sit with me more and asks to do stuff with me again. I would just make sure they know they are still loved just as much and you’ll be fine…
what if you wait till said child is 10 years old do they still do that? I want another baby but fear this would happen
Hes jealous, duh. What have you done wrong? Nothing. You do need to acknowledge that he feels some type of way though since someone else is taking away from the full time attention from your 4yr old. Plan to take him somewhere just you and him for a couple hours. He’ll come around eventually.
I introduced my baby to my 2 1/2 at the hospital let him hold him. He said " mine" I said our baby. He helped get diapers powder and put sox on Ben. I gave him a baby doll before his brother was born. He held his doll while I fed Ben. Hes a big ass man now
Make more of a fuss of him than the baby when he’s around…
He’s jealous of the new baby. Give him time
Completely normal, he has feel like his been replaced. Just keep showing him mummy is still there for him. He will come around. Maybe make some time for just you and him so he still feels special. You haven’t done anything wrong. His just got his nose out for joint because his number one person for the last 4 years he now has to share. Big feelings to work through here
We do date nights with older one. Also, you can make him feel involved if you give him easy baby care tasks
Include him in any way he can help. Throw a diaper away, talk to the baby … small things to make him feel like he’s your big special helper.
He will have to adjust… its early still. 
Have you let him feed her yet Ave him help you with her getting clean diaper and wipes