This is why I wanted AP we DO speak French at home when possible- I am not a native speaker though so it's never quite the same.
What do you mean "when possible"? Does your partner speak French? If so, it should be possible for you to speak to your children in French most if not all of the time when it's just the four of you together.
If your partner is not conversant in French, then you can speak to your children in French when he/she is not around.
I grew up abroad and had a number of friends from bi/multi lingual homes. Generally speaking, the parent who speak say, French, would speak to the child in that language at home and if the other parent also spoke French, conversations at home would be conducted in French.
Outside the home, the child would converse with others in say, Italian (learned at nursery, from friends, the TV).
Back living in the UK, I have a friend whose partner is South American (Spanish first language). Friend has also learned Spanish to a high, if not fluent, level. At home, when all three are together, they speak in Spanish.
If friend is alone with child, they speak in English. If friend's partner is alone with child, they speak Spanish. Outside the home, child goes to nursery and watches English tv. All her outside interactions are conducted in English.
What the parents did not do was helicopter some Spanish au pair into spend a few weeks a year with this child and expect the child to be willing and able to converse with the AP in Spanish, having received little or no groundwork beforehand.
If you want your children to speak French, you should be willing to speak French to them in the first instance.