For parents
Ages 4+
Two pictures with four things changed between them. Your child taps a difference in either picture and it is marked in both, so there is no holding one half of the screen in mind while looking at the other. A tap anywhere else does nothing at all.
Nothing counts against your child here: no penalty, no timer, no counter going down. The count only goes up, which is what lets a round be put down half-finished without having been failed at. On a phone the two pictures stack rather than sitting side by side, which makes each about two-thirds wider than it would otherwise be — enough that a difference can be big enough to tap without having to be a quarter of the picture. On a wider screen they sit side by side.