Does this make sense to you?

I can understnad why he is your ex. Tell him that he needs to take some responsibility for his children and pay the lawyer fee himself.

Hi! If the reason for his wanting you to pay is because of the possibility that your not signing in the past caused him extra expenses - only then does it make sense. Otherwise he seems to be taking you for a ride...

I'd tell him that he must pay his attorney. The fact that you have the children on a daily basis and take care of their every need. You buy everything they need. That all he has to do is pay a paltry, small, no where near the amount needed to child suppose payment and their needs are left to you to get. That the least he can do is pay his attorney. That it's in his best interest as well as he left the children with you and you must care for their every need and when they are sick or hurt you are the one with them. When they cry for whatever reason it's you that take care of them. He has his freedom to do as he wishes, since he doesn't have the children on a daily basis. He can come and go as he pleases, not having to think of the children and their needs. The least he can do is pay his attorney. Tell him you could take him to court, making him miss a day of work and have the judge force him to sign the papers. He would then be made to pay your attorney and his since he is working. Tell him you are taking his schedule into consideration as well as the children needs. Sign the paper and and pay his attorney or a judge can settle it all for you two, and he would come out having to pay both attorneys.

maybe he has the reason for it,who knows whats behind the screen

yeah it does. he is making sure that you do not have legal custody so that he will not have to pay child support. He is stalling.