Well, maybe don't do it? Maybe not until they are 12yo or something like that? My feeling is many parents don't want to parent at all and so they delegate to smartphone, tablets and TVs. Parents should go back to be more...parents.
We don't have an ipad exactly because otherwise my 6yo would like to play with it (her friends have one) instead of going out and play outside. In my opinion children should not have a smartphone, do tangible stuff and games.