As a young single male my thoughts on this probably count for squat, but I think that young kids should have access to technology but *only* under direct guidance. It should never be used to "shut them up" and it should be rationed when used as a toy.
My reasoning is that while there is *huge* benefits for the child when guided through enrichment activities it is detrimental to allow your child to simply vegetate (mostly mentally, but also physically) with these devices in their hands.
Spending time *with* your child and using these devices to get a head start on reading, writing, critical thinking, general knowledge/worldwide culture is basically the direct equivalent of guiding a child through their school homework. It's bonding, entertainment and education all in one and not in a terribly lame way! (like most "educational" games). As a child that did not get the privilege of having help with my homework (but occasionally with other things) I can vouch for the difference this makes.
You should not be forcing the child to perform to a high academic standard during this time (thus making it a negative experience). Just make sure they are thinking by asking them about what they're seeing/doing and introduce stimulus material where you can.