One great way to help your children learn the days of the week in French is to either make a calendar or better yet, you can put the day of the week each day on the fridge.
Make a pretty (or basic it doesn’t matter) sign for each day of the week. You can do this part with your child or without. Then, every morning as part of your ritual, you can hang up the new day of the week on the fridge and say it together a few times. After a while, they will be changing it for you to the correct day. I did this right before I gave my kids breakfast so that they had something to think about while I was pouring milk in their cereal bowls.
Here is a list of the days of the week:
Lundi – Monday
Mardi – Tuesday
Mercredi – Wednesday
Jeudi – Thursday
Dimanche – Sunday