When I was I suppose about 4, I had a whole load of imaginary friends....it's quite a common phenomenon at that age.
How the brain develops in a kid is an interesting thing....my older son similarly had a range of invisible chums, I'd have quite long conversations with him about them and what they were up to.
Undoubtedly too much early exposure to electronic fantasy worlds is likely to inhibit such processes in developing imagination, but who's to say short periods will.
It's not only relatively common but there's a lot of research to suggest imaginary friends are beneficial to development.
Even more interesting is that some psychologists believe they live on until late adolescence, they just don't engage so often due to stigma. There are lots of "Ted"s out there, apparently.
Unfortunately, a lot of research into how early exposure to technology will affect children is non-existent, because the kids you'd study are quite obviously still kids... It's also hooked into a large amount of media scaremongering, Piagetian theory, and lovely but non-scientific anecdotal "in my day.." stories.
Another issue with these "findings" is that they are largely predicated on the assumption that if you let a kid play with your ipad that's the only stimulation you ever give it, which from what I know of most prevalent parent TEFers (and anyone else I'd voluntarily associate with) is clearly bollocks.
What is very convincing from research, I believe, is that creativity in particular forms best when all senses are engaged (I.e. In the real world) as opposed to what we currently experience via technology. In that case, I'd say an ipad was more than sufficient, but I'm not a parent, nor do I know what's really out there.
Disclaimer: provoking me into a discussion about psychology is like asking Reg to talk about the Tories.. I'll shut up now.
Just do the opposite of whatever Tans says.