I've not the faintest idea on the foam, but the spray paint will be safe if you seal it. Super glue would most likely work better and is again safe as ling as it gets sealed with the paint.
seal it?
With a clear coat of some kind. What was your idea with the foam? That might be the best idea depending on what you had in mind..
With my hides i used mod podge hard coat to seal it. as for foam i used some that i found at lowes. It was like 6 sheets for 9$. Its in the same isle as the insulating foam.
His idea of using grout is the only reason I think styrofoam would be a good idea. I wouldnt recommend just painting it, even if you seal the paint. The grout he's using is whats keeping it from flaking apart. And its thick enough to fill the crevices in the foam, which is really important. Just painting it wont do that.
If you planned on using styrofoam, Id probably stick to exactly the way he did it. You can get a nice clear coat in a spray can at any hardware store.
That is a rubberized sealer. Like on the informercial. All you'd need is a clear coat. Similar to this
http://www.acehardwaresuperstore.com/1512-clear-lacquer/50913.html
As long as its nontoxic. Just go to your local hardware store and ask for a nontoxic varnish/laquer
Can you use modge podge?