You can make veggie rice krispy treats with marshmallow Fluff, but I don't know about its dairy properties.
Fluff is made with egg.
Vegan treat recipes:
Hmm. Most of the ones I can find online are more "adult" type, with things like green tea or cappucino flavor, rather than chocolate and rainbows. As for Trader Joe's, the JoJos are vegan, as are some of the chocolate covered pretzels, and they've got a few flavors of vegan ice cream. If you want to go the ice cream route, then I'd recommend getting one of the Turtle Mountain brands -- So Delicious or Simply Decadent. The coconut milk flavors are awesome, and the soy flavors are really good. (I think a preschooler might be happier with the soy ones, actually.) Most regular grocery stores will at least have one or two flavors of those, either in the regular freezer section or in a "natural" section.
While I'm thinking ice cream, the Smucker's marshmallow syrup topping is vegan. Trader Joe's brand chocolate chips are vegan, and there are a ton of chocolate chip cookie recipes out there.