We also live in Maine! Thankfully my boys, 7 & 8 love going outside in any weather. I really do not like going out in the cold months at all. But they will happily go out and play. We have those in between weather times too. They will take out their play guns and go hunting (we live in the woods). I know not everyone does the gun thing so that may nto be an option for all of you. They play tag, football, baseball, soccer. They also love to play with the dogs outdoors, we have two large breed dogs. Hide n Seek is another favorite game. We also have a bird feeder on our deck, so that is a constant source of entertainment. Especially since I’m not a big fan of birds. So it’s always fun for them to announce “Mom the blue jays are back!” lol
I also for general exercise will just have them go out and run laps around the yard. This also works for consequences for misbehavior. Or if they have only stayed out a short period of time, I will say “first you need to go and run 10 laps around the yard then you may come in.” . Warms up their blood and gets their heart pumping. Great exercise. You could also play Simon Says outdoors with the children. That is fun, and works on immediate obedience in a fun way. Also can be played indoors.
We have had such mild weather so far here in Maine for December… I”m loving it! My sister lives in Wisconsin though and said it has been cold!