Start with Facebook's reporting procedure for just this situation, particularly where pictures of children are involved. Deal with the picture, first, before escalating the conflict.
While I doubt what you've posted is criminal (You do say "lot of problems) a report to the police about anything criminal in nature is a for sure. If there is any stalking or cyber bullying, report that too.
If the pictures are your pictures because you took them and can be said to be the copyright owner of them, you may want to use the DMCA Take Down process to get them blocked or removed. Here is link that explains this (I cannot vouch for all the content herein):
That said, there is nothing illegal of course by her doing that unless the pictures are illegal in some way (pornographic for example), but that of course is not what we are talking about here. What can be illegal is harassment. If her behavior is so egregious you may consider talking to the police and even filing s small court claim against her for harassment. Of course, the court will really want to see that it was bad behavior and not just nonsense. I will tell you that the courts will not look kindly on someone that uses a person's child to attack them or harass them in some way. So if she has no good reason to be posting these pictures it will not look good for her.
DO NOT attempt any kind of self-help. As a general rule: DO NOT ENGAGE CRAZY! Go to police, take or her to court. Don't call, reply, visit, etc. This will only end up landing you in trouble as well.
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I cannot agree more with Frank Natoli's advice about leaving out the crazy.
If your boyfriend used a lawyer in his divorce, have him contact that lawyer to have them get a restraining order against the Ex.
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