Once the payee endorses the check both ways it's a bearer instrument and there is no real restriction on where it goes.
Regardless, I would not accept it unless I had the children's fiduciary accounts. After he had endorsed the item both ways, I would accept it for deposit into those accounts. If he is due some of the monies, he can withdraw them.
I want a paper trail...
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In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.