I'm currently making a School Days coat for my daughter. I read through this entire forum to see what tips I could glean, and the two most useful things were 'don't use leather to attach toggles', and the awesome suggestion of using magnetic snaps. I love the magnetic snap idea! sooo much easier for a toddler to operate!
There seemed to be a lot of people who had problems with either leather breaking, or the cotton cord fraying on the toggles. I just wanted to share my suggestion (I haven't done it yet, so don't hold it against me if it doesn't work!). I've just ordered some round waxed cotton shoelaces on ebay in a colour which will hopefully match my wool coating. Shoelaces are available in a very wide range of colours, and if they're designed to live through being laced in shoes, surely holding toggles won't be a problem for them.
I'll probably be back when I've got a bit further with the coat. I can't do too much as I've ordered some fabric from Spoonflower to line my hood and do the quilted lining in. The rest will be lined in normal silky lining fabric for ease of wearing, but I don't want the hood to fall off her head.