My child express she didn't want vaccinated: Advice?

Looking for advice. I have two children 5 and 8. The 8 year old received her covid shots back when it was approved, I think she was 6. Could be just a coincidence but since then she’s developed some medical conditions. But us very apprehensive and does not want another covid shot. My ex husband is pushing very hard for my 5 year old to get her covid shots and she just doesn’t want to do it. They’ve both had covid before. I want to be respectful of their wishes, I appreciate they are being vocal and expressing their feelings/opinion but my ex husband is being relentless and won’t drop it and even has been saying to the children “you will get the covid shot.” “It’s not an option.” “You’re going to do it.” It should be noted that they both have had their flu shots. If anyone has had a similar situation with their children not wanting the vax and their spouse/ex not wanting to budge? Do children get a right to their opinions on their body or do parents automatically choose for them? We are at a stand still here and I feel the children should be heard and their opinions/feelings respected. Thank you in advance