Acetone can melt plastic so I'd be very careful using it on toys.
I use non-acetone nail polish remover. The results are varied though.
I used non-Acetone nail polish remover to remove the giant blue trapeze on the Wet-Suit torso that my Hiryu custom uses:
http://www.joedios.com/dioramas/sho...r&imageuser=270
And while you can't see them, I also used this product to remove the "badges" that were on the 91 Grunt's jacket to make that Clutch custom.
I usually just put some of the nail polish remover on a Q-tip and rub it against the paint I want to remove. Sometimes I use paper towels to rub too. It depends on the area.
Just be careful using this stuff.