If a child becomes lethargic in winter and complains constantly for no reason, that could mean, that he is experiencing winter depression caused by the lack of sun. The best recipe for winter discouragement is playing together with peers and parents. Take out games and toys that you have forgotten in summer.
You should also take care of the proper lighting of the child's room. It is worth using every glimmer of daylight. Heavy, Replace dark curtains and dense curtains with light curtains, light and transmitting more light.
Use your long evenings to plan your winter vacation. It doesn't have to be a long trip, a np. longer trips out of town. Take a look at the maps, read the guides together. Such conversations chase winter sluggishness out of the house.