I think n1as pretty much nailed all the points. You're probably not going to be wanting faster than f/4, so it's questionable whether a prime is even appropriate. (Although I shoot primes almost exclusively, I often wonder why...)
I haven't seen mention of the 24-70 which is a good combo on the APS-H sized chip. My other suggestion would be either the 100/2.8L macro or the Zeiss 100/2 (assuming you can focus manually.) I had a 100L and now use the 100/2... both are first rate optics that work well with the 1D3 and 1D4.
Finally - I've shot kids using a 70-200 /2.8 with and without a 1.4x tc. With kids, this allows you to get out of their sphere of interest and they behave a lot more normally.