I work with a lot of schools, as well as parents who have children with special needs, and I've seen a lot of adults loving the Griffin Survivor (a real favorite), Trident Kracken, Otterboxes, and Gumdrops cases. But many cases have downsides: soft cases (like some from Gumdrops) can be a problem if your child likes chewing on them, and some kids get obsessed with unclipping claps, such as on the Kracken (reports are also that some cases open on impact, when dropped). Seems most cases have an achillies heel (or two), and the perfect case varies depending on the child.
Many proven iPad cases in the $20-$30 range can add home button blocking functionality with the simple addition of inexpensive BubCap home button covers.
While several cases that are not yet available tout designs that block the home button, those cases are a bit pricey ($50-$65), and probably most parents with an iPad and a toddler don't want to wait several months for the product to become available. Once these products are widely available and tested by the public, they may prove to be the way to go.