Mobile games are largely for adults IMO. Most games operate on the free to play model which leaves the less financially capable out of top tier play. The games are also designed to be played in short burst rather then longer marathon sessions. This style is better suited for adults on the go, either on their lunch break, morning, evening commute or whenever kids otherwise distracted. Games like Clash of Clans, Hearthstone and Minecraft can and do attract hardcore players, but because mobile gaming has such widespread adaptation I would say that on a whole, it's largely comprised of casual gamers.