Should I ask my ex why he stopped seeing his son?

My boyfriend and I have been together for over a year. We have a baby due on April 2 via c-section. He has two teenagers and a three-year-old from separate mothers that we see every other weekend. Recently, he was supposed to meet with the 3 yr olds mother to get on the same page as far as discipline, but she never showed up. The weekend we were supposed to get the 3 yr old, I asked him to text her and make sure we were going to get him. He told me he did and that he was waiting for her to text him back. When I checked his phone, he had never texted her at all. Up until recently, he has been adamant about his youngest, but it seems like he has given up. We have not seen the 3 yr old in 2 months. Should I ask him why he lied and why he never got ahold of her? Or should I keep out of the whole thing?

I personally would. I would be curious