This doesn't quite fit your description, but Homecoming (http://ksarchive.com/viewstory.php?sid=4527&warning=1) by Beedlebarg, has a great section (in chapter 2, so hang in there) with Spock being a wonderful, adored father to their toddler son, while Kirk doesn't even remember them. It's got some other good moments depicting Spock as a natural, loved father as well - it's one of my favourite kidfics, so I hope you like it.