I'm not a parent, but I know my sister used to get her kids involved in a number of activities at home during the summer that they loved.
One involved writing their own newspaper. They had to think up stories to write, interview people, research a topic, or just get creative. They compiled the stories and handwrote them, published the paper, and sent it to relatives. Later they did it on a computer when they were a bit older.
They also wrote plays, acted them out, and filmed them with the family camcorder. Again we enjoyed them with the entire family at gatherings.
Writing, grammar, spelling, creativity, problem solving, etc. were involved.