Okay, I know that is an age old adage, but it’s true. Children are wired the same as adults and need to practice their new language every day. It’s easier for them and for you.
If you took a foreign language in high school or college, I’m sure you understand what I mean. During the summer break, you probably lost a lot of what you learned. So when you started back with your language classes, you had to review a whole lot of what you previously learned.
I am not saying that you have to do a whole lesson a day or anything like that. I’m a mother too, I understand. Some days you just try to make it through the day. But on days like that, you can still just do little even if it’s saying ‘Bonne Nuit’ at night to each other and to their stuffed animals.
My advice is to just let them hear the language on a daily basis even if it is only 1 phrase. They will remember that it is ‘French’ and what they learned on other days.