Why do you say that?
A child born in France is a citizen, and so cannot be deported, and since a child needs parents, his illegal parents aren't going to be deported either. At least that's the legal reasoning in Cheeseland.
From the EU website detailing such matters:
French nationality
Any child born to at least one parent who is a French national has automatic French nationality (whether born in France or abroad).
A child born in France, where neither parent is French may receive French nationality (on request) at age 18 years if they are resident in France.
A child who has lived in France for at least five years from the age 11 onwards may receive French nationality (on request) at age 18 years.
We - are as far as I know -the only nation with such a policy.