You really have 3 options... IMO


24-70 is a great lens if you think it'll be enough reach, best best is to honestly maybe rent it and try it.. or just go into a store and bring your camera and try it out.


24-105 is the next best thing and others will argue possibly better, especially with the IS if you're moving around trying to capture the moving child.


70-200 4 IS is about your budget currently, before taxes.. same with the rest of them really.


2.8IS is great ... but it's way over your budget and might be too heavy for you to carry around all day at the park, etc. But I love mine





But those are pretty much your options IMO for the price. The 2.8IS is $1800 use if you're lucky.. and well over $2k if you buy it new.. + taxes.