A.
Just remember that whatever you purchase, kids are gross. They will inevitably wet the bed, puke in it, and do who knows what else... Plus, they generally don't weigh enough to need all the extra support of a fancy mattress until they are much older and have generally outgrown the peeing/puking/pooping in the bed thing. We just purchased a fairly inexpensive set (about $150) for my daughter, knowing that we will replace it when she gets old enough to need the support.