This website has a lot of resources and options for parents who want fun ideas, and includes free printables in both English and French. You might have to click around a little to find the versions in both French and English.
Here is an example of a math place value game which you could play in English and then play in French:
Duolingo is free, but you can purchase a subscription. Duolingo teaches vocabulary, similar to flashcards or self-quizzing, but adds more games than some other options, and includes more grammar. The vocabulary seems to be presented in a different order than other apps. It teaches beginning skills but does not have conversation practice. Available on computer and app.
Bingo games are a great way to get young children to pay attention better when learning a new language. The game description says, “Reinforce French vocabulary with a game that utilizes auditory and visual learning styles. Players see the image, the name of the item in French, and hear it pronounced by the caller. Pronunciation Guide included. 2 to 6 players.”