We have two tablets, but they are not "theirs." They use them, but they aren't responsible enough to use them without supervision. We havea lot of educational games, we'll use spelling city this year, possibly brain pop. They can be great tools, but there's also the possibility that it's just another game device.
My son has an iPad mini. He has a bunch of Aps but his favorites are Teach me Kindergarten, the Reading Eggs and their Math ap, WordWorld, and the animated stories from Sandra Boyton(he has the matching books so he has memorized the story but likes that he can make the animals come alive on the iPad). He also likes Numbers with Nemo and the Sid the Science Kid ap. I just got him the Hooked on Phonics ap when it was free a few months ago but he's not used it very much just yet(he's only 4.5).