My wife and I leased an i3 when our son was 11 months old. He's now a little over 2, and she has been transporting him every day to daycare in the i3. Neither of us is very tall (5'6"), but we feel there is plenty of room in the front passenger seat with him behind. Our infant car seat is a maxi cosi mica, and we have a peg perrigo convertible. With an infant seat you remove from the car, getting it in and out was no problem. I will say it was a bit awkward getting him into and out of a rear facing convertible seat, but you get used to it. Now that he's forward facing, it's no problem at all.
My biggest gripe is the reverse hinged rear door. No problem if you have plenty of room, but if you're in a tight parking spot or in a garage, it can be a PITA as you will be trapped and have to squeeze forward into the front door to close the back door then escape, all while holding a baby, diaper bag, etc. That aside, we absolutely love the car and are already talking about getting another one.