I haven't used the home depot brand but I have used a dry erase paint that I ordered from www.smartersurfaces.com for my home office. Works just like you said in your school so it should work OK for a playroom, just make sure your kids know which wall is painted!
I have heard the same about the HD brand (not sure but I think it is rustoleum). It would be worth the effort to buy it from someone with a little more specialization in these types of coatings. The paint used on the schools is quite a bit better than what HD carries. Pretty much all their paint is that way, regardless of what the TV adds and the people who get paid to sell it say.