What's wrong with kneeling down, facing the threat with your hand near your BUG? In this position you can still hold your ground and keep your child close. I doubt the aggressor would think you were preparing yourself to draw your weapon. Your weapon stays concealed and you have the advantage.
Remember there are no rules to protecting your life and the life of your child. You don't have to stay standing the entire time. Crouch as if tying your shoe, force your child behind you and hold her with your left hand while your right hand dangles near your rig. Or something to this effect that will give you the advantage in the situation at hand.
There are times I leave my house with my g27 on my ankle and nothing on my hip. When I do its because I have athletic gear on. (Sweats, wind breakers, softball pants (of course my gun goes in my ball bag/truck while playing)) I feel very comfortable having my gun on my ankle. If a situation like this rises everyday then I would keep my gun more available but these things happen very rarely and mostly end without problem. When the problem does arise I will likely do as I stated earlier.
This is my opinion and I hope it helps.