After having purchased two 20" tubes by another brand from the local bike shop and having them fail, I have been very satisfied with the Bell 20" tube I purchased from Sports Authority. Not only was it 1/2 the price of the other product it has actually last more than two weeks on my daughter's bike without rupturing.
I would recommend getting the tubes filled with slime. My son rode his bike once, and it popped. His other tire tube has slime, and it's fine. Unfortunately, our local store doesn't have a great selection of tubes. They always seem to be out of the ones we need.