As Artrage is a simulation painting prog there is not function "filling with paint"!
But as there is "stencil" it's not so difficult to put a stencil over something and paint with a big brush :)

Does trackmania has always a free version? (kids have used that some years ago)
Funy of this prog was the possibility to build the race track

problem of all the animation render for kids is the Interface!
I believe there is only one http://www.cosmicblobs.com/software/deluxe.html
But maybe it's too basic?

For the french interface words were choosen for their length under the icon! It was a task :)
English is so compact! See the German or Spanish version, but champion are Dutch they suffer ;)