Hey if we are going to redefine childhood to age 26 for insurance purposes, why stop there? Lets change the voting age to 26 and the smoking / drinking age to 26 as well. In fact why not add another mandatory school above high-school for ages 18-26. Of course mandatory curfews and driving restrictions would also apply.
I can hear the young adults screaming bloody murder already! But the fact is, you all shouldn't be able to have it both ways. If you want considered a child to stay on your parents insurance, then you should be considered a child in all other facets of your life as well.