The muscle cramping (leg & arm pain) started around 6 yrs old for my son. He is 7 yrs old - 8 in Feb. He definatly complains more about it in cold weather and it is brought on by muscle cramping. He went outside to play last week in our first significant snow here and he came back in 20 minutes later with cold painful cramped rock hard legs. I wasn't thinking and should have put snow pants on him. Same thing happens when he swims in water that is too cold. Over doing it will also bring it on regardless of the weather.
Yes, it is the same for Matthias. He wears long underwear a month longer than I do on each end of the winter, and he loves wearing snow pants even though it hasn't snowed yet, because his legs cramp so quickly when he gets cold. It is the same for swimming -- if the water is 90 F he is happy! In public pools, he goes back and forth to the hot tub whenever he starts to cramp. When he cramps, rest -- forcing him to keep walking will make it worse. If he can still move it, gentle movement sometimes helps, but not if it's really painful. Often after a short rest he will be okay again, but not if he is getting colder. Use blankets or hot water bottles (not too hot) to warm up once you get home. A warm drink helps too, to bring up his core temperature. Matthias always fought me about walking, and once he learned to talk he could tell me it hurt if he overdid it. Motivation has something to do with it, though, because he's done some long hikes without cramping when he really wanted to, and if he fights about walking he can cramp in a block or two even when it's warm out.