I live in MIchigan.. and this is what you really need.
Snow pants. you can get these at salvation army for $5. The bigger boys wear out the knees but little ones dont wear them that much and the used ones are fine.
2 or 3 pairs of mittens... 2 pairs should be thick and waterproof- good for playing in snow. 1 pair for just keeping hands warm on the way to school.
3 coats. one should be thick and warm (will probably wear this in dec, jan, feb), one should be medium weight fleece lined with a windproof outer layer..(wear in oct, nov march) and a lightwear jacket fleece is good..
snow boots.. I do not buy snow boots ahead.. they need to fit in january and february.. I cant predict shoe sizes so I dont buy boots till we need them.. bootyonly buy snow boots when it is almost n
a hat or 2 .. for cold days playing in the snow. I buy coats with hoods so my kids only wear hats if they are outside playing in the snow..
most days my kids just wear a coat.. we go from house to car in garage.. and then we go into the school or wherever we are going.. we only wear hats and mittens if we are playing outside/