You can't use it in court.
Why does he want it off asap when he gets home? My son is very allergic to the chemicals in them and could never wear it. Just smell it take a big wiff. How can it be great? Your nails absorb things just like any part of your body. I have seen people who have worn nail polish for years and their nails are stained yellow or red. or they have fungus problems from years of polish or fake nails. Natrual is the best......always I would maybe check to see if the reason he wants it off is because it bugs him. the smell. ask him. Or try to find nail polish that has very low chemical content health food stores.
I agree completely with mammo. This is very typical. I mean absolutley no harm by this but I want you to know that brining this up in a court case, particularly a custody case will seem as if you are a little desperate, and are as they say in court, reaching. I understand your concern, especailly if you are the boys father. It is nice to see that you care, just make sure it is not for spite.
Little boys this age usually want to be like mommy when they see her painting her toe nails, and want theirs painted too. It's not a risk to him, and I'm sure it doesn't happen that often. It's truly nothing to make a big deal of.