There is a discount shop near me that has 'high school musical' kids sleeping bags for $5 atm. The pic is pretty big though, so you would have to like high school musical.
After HotI told me about these we stopped near that store the other day, i popped in and got the girls 1 each, they will keep them warm but are not the greatest quality if you want them to last forever but for $5 i figure they are just going to end up dragging them around a campsite or using them at home anyway.
Once they are a bit bigger i will go out and buy them a proper adults single sleeping bag.