"My father and I play soccer on the weekend."
I don't think it should be wrong. In Chinese when there are close personal relationships you can omit the "的," but it doesn't mean it is wrong when you include it. It just is not necessary. Some of Duolingo's exercises recognize this and accept both, in this case they are not. Maybe with the exception of the exercises that teach the "omit 的" part of the grammar, it should accept either.