When the family goes into town, the weather is snowy and cold, then when the plane takes them home again, the landscape is shown during spring breakup, and then it is snowy again when they are back in their cabin.
When the girl goes out on the front step to look at the snowy landscape, there is no snow on the porch or the cabin, and both she and her little brother are too lightly dressed to be comfy standing there if the weather was truly cold enough for the snow to have coated everything in a heavy sheath of white.
After Toby falls through the ice on the lake, his parents give him a hot bath to warm him up. As he stands after the bath to be dried off, Toby is clearly wearing swim trunks.