Before watching the movie:
I get a sense this movie was conceived as a response to the success of E.T. Instead of an alien hiding in a suburban family’s home, it’s a sasquatch. This time around the entire family is in on the secret (and the dad seems to be the one taking point on how to handle hiding him), but there’s still government people looking for him and he can’t stay forever. Not a total knockoff like Mac and Me, and produced by the same companies, this might be more of a spiritual sequel.
I know nothing about what any of the family does other than John Lithgow, but I assume the kids play with Harry, do cute kid stuff with him, and are generally the main catalyst for sasquatch antics.