Been there. My girls are 2 and 4.
I'd say skip the shoulder bag, get a Lowepro Flipside 300. It's a backpack, which IMO is more comfortable for wearing all day. It will hold your current kit, with a thinner slot for what, IMO, should be your next purchase - a 430EX II. You should be able to get one more lens in there, too, when the time comes - it'll save you from buying another bag later (I've got more camera bags than my wife has purses).
One other recommendation - a Blackrapid strap. Once they start moving, I found the neck strap with the camera in front got in the way of a two-handed kid grab. With the BR strap, the camera hands out of the way at your hip, leaving both hands and torso free. You can also wear the strap with the backpack.
Hope that helps...