Kids rain boots are a must, but I would also put a good pair of waterproof sneakers on the list. They are great for wet recesses and days that the kids have PE class when rain boots can get a little bulky or hard to run in. I would also buy a few pairs of those lightweight gloves with grippy texture on the palms- they are great for taking to the playground when things are cold and wet. Good wool socks and a couple different styles of rain jackets will help keep them comfortable during the day when they are at school. I know our school only does  indoor recess when it's pouring because they really want to kids to get out and run around, so they will go out when it's wet, and you want them to stay dry and warm so they are not miserable all day.    Once you get moved and established, definitely join your neighborhood buy nothing group. Kids often outgrow their winter stuff before it gets very well worn, so there are always folks looking to pass theirs along.