Used to be. Disobedience of most court orders turns the matter into criminal, orders are not optional. If a judge doesn't want an arrest for disobedience they specify in the order what action will be taken as an alternative, i.e. "failure to comply with this order will be addressed at our next scheduled hearing".
A child who is missing sure as bananas results in a search. It would likely result in a warrantless entry if the reasons can be articulated. I would think most any LEO should be able to articulate, "the guardian who previously had custody time was present, the child was not. The guardian who currently had custody time was present and had not seen the child. The guardian who previously had custody time said they didn't know where the child was. Based on these circumstances, I believed the child was missing." I can't imagine any LEO showing up at a missing child call shrugging their shoulders and leaving.
IDK, man. I think it's a stretch. When I went through my divorce I was very in tune with what goes on and numerous people report not being given access to kids and LEO referring them to the courts.
"Missing child", whose whereabouts are unknown is a different issue. I'm assuming mother is custodial guardian, who may not be inclined to give details to an ex who obviously has some issues with self control.