I started doing Duolingo. It’s good to challenge yourself. I picked French because I took it in school and I wanted something I would be successful at. If your child is taking a language in school, you can use Duolingo to keep them sharp over the summer. Or just to help them learn a language.
Another thing you can do to aid in second language acquisition (because I teach English as a foreign language too) is to watch TV shows and movies in the target language. That way you can learn how native speakers sound so that you can sound more natural. And it doesn’t feel like working since you’re watching TV.