My 26-month-old is tall for his age, and he fits in his SleepSack just right. He's been wearing them for about 6 months, and sizing has been acceptable the whole time. We have 2 fleece ones and one "basketball shorts" thin, perforated one.
I love not having to worry if he's kicked his blanket off in the night, and I'm glad they look kind of dorky, because it shames me into getting him dressed before midmorning.
This is a great deal, too, especially if your kid's into Disney characters.