Help: Do you use a single or double thread for the binding on a childs quilt?

I do single.

single - just with tiny/close stitches.

If it is for a child I machine the binding. No hand work. It's more sturdy.

Double for all quilts.

I machine stitch all binding and sometimes use a decorative stitch just to add a bit of fancy. Machine stitching is more sturdy and won't come loose as easy. I can machine stitch a binding on a twin size quilt in less than an hour (I also use a glue stick to keep the binding right where I want it) and then the quilt is ready to wash.

I usually do a double fold binding and hand stitch the back with single thread. I do use a sturdy thread to do it. If you use double thread, you have to constantly ajust the loops that form when one thread pulls tighter than the other. I do like to use the all machine binding that Charismah did a tutorial on, for quilts that will get a lot of wear and tear. They look real nice with the little flange piping on the front. The tutorial title is "Quick Machine Binding With Flange".

i would put it down with the blanket stitch on my machine

If it's for a child, I definitely would machine stitch the binding (unless you're making an heirloom piece). Not sure about all makes, but there's a bi-level binding foot for Pfaffs that makes it so easy. You don't even have to pin or glue or anything. Takes a bit of getting used to, but it's the best $20 I've spent in a long while.

Attach double fold with machine and finish by hand. I add a knot every 2-3". Well sewn hand-stitches are sturdy and can easily take abuse.