Our experience of schools in France has been very positive.
The schools are happy to accept children who speak more or less no French, help them adapt and fit in, and give them a top class education. Many departments in France have special teachers who flit from school to school giving French lessons to new arrivals.
The French education system, like the health system, is held in high repute (but note - the French government receives a lot of criticism that the education system doesn't adequately prepare children for real jobs and working life).
We have little criticism of the French system. Perhaps the 'equality of teaching' hinders the progress of the very brightest children, or leaves stranded the least gifted, but generally it seems to work very well.
In larger cities it is possible to find International Schools which teach in English, but younger children will benefit more, I think, from attending a 'normal' local school.
There is a danger when there are too many expatriate children in a school that they gather together, speaking English, and fail to integrate with the local children. Some children appear more inclined to this than others. More commonly, expatriate children seem to provide a 'curiosity' to the local children, who accept them rapidly into their circle.
It is often said that a child will be fluent at French after a couple of months in a French school. More often, after 2-3 months the child can speak French plausibly, but it needs 6-12 months of immersion to be considered fluent, sometimes longer. This process is longer and harder for children over about 10 years old.
Other features of the school system in France
See also a description of the French school system for more detail
There is a lot of focus on the key subjects - Maths, French and English, and less on the arts and other subjects. French grammar and use is taught every day, and children have to learn (and recite to the class) poems from an early age (6-8 years old).
Wednesday afternoons (or all day Wednesday) are often free, and this is when children usually pursue sporting and musical activities.
Packed lunches do not exist - the children eat school dinners or go home to eat. The school meals are usually of good quality.
The school holidays are long - overall, the longest in the Western world, I am told. But the school day is long also, typically 9-4.30 at primary school and 9-5 at upper school (age 11-15).
Related sections: An introduction: Living in France
Financial considerations: Finances of moving to France
Moving on a limited budget / how little money can you move with: Relocating on a budget
Language considerations: problems with learning the language: Language problems for expats
Meeting people and becoming established: living in a French community
Schools and education: expat children in French schools