He wants to have his son with him 2 to 4 weeks Will he bring him back?

My grand daughter & her husband are separated. Divorce is in the plan. Nothing legal is set up yet. They have a 3 year old. Could he be held accountible if he (hus) doesn't comply with the agreement to bring child back on promised arrangement?
Update: What about a promatory(promise)note and notorized. Do you know if that would hold up in court. Since those notes and promises seem to be meaningful in other court cases.
2 answers 2