score:3
France has staggered school holiday periods for the February/March and April/May vacations: one third of the country goes on vacation for two weeks, another third goes on vacation the second week and the week after that, and the third third goes on vacation the third and fourth week. The purpose is to spread travel and holiday resort occupation around. This means that finding a time when no place in France is on vacation can be a bit difficult.
The education ministry is the reference for vacation dates. The site is in French but dates should be easy to parse, if not you can find the same information on many English language websites. You can also find the dates of public holidays on Wikipedia and elsewhere
If you can't find a good time, you should at least avoid the school holidays for the Paris area, i.e. zone C. I don't know if it'll help much as some people travel far (even from other countriesβ¦) to visit Disneyland.
Next autumn, you're in luck. The French autumn break ends on 1 November while the Belgian autumn break runs the following week. 1 November and 11 November are public holidays, but Friday 6 November is a normal school day in France while it's a vacation week in Belgian schools.
Upvote:2
I read your question as in 'which part of the Belgium summer holidays' is the best time for Disneyland in Paris. In that case, July and within the week, a Monday or Tuesday or a Thursday or Friday. See this page by Disneyland Paris. I guess the earlier in July the better as more countries get holidays in July and most do not get the whole of the month.
That is confirmed by this page.
mid-July to late August are very popular.
If you do not want to go in the summer holidays, try to find a public or school holiday in Belgium that is not a public holiday in France.
Edit: On reading the new version of the question I took out the 'list of national holidays' in my diary for France and Belgium. No joy there, all days mentioned for Belgium are also mentioned for France, (besides July 21, which you with good reasons do not want.)
July 11 is 'de dag voor de Vlaamse gemeenschap' (The day for the Flemish community.) This should be a day of for you, school holiday already for the young one and is early(ish) in July, but you ruled out the summer holidays (which I understand.)
The autumn holiday for the schools in Flanders is rather late in the year, but might work for you: 2 till 8 November 2015. I guess that even if there is a school holiday in France at the same time, you will find the park so much more quiet than in the summer. If you do not like that idea, the next likely option is the Easter holidays, where the Flemish schools two weeks: 28 March to 10 April.
A better option, in my view, is to talk with the parents and ask for a day the school of your godchild is closed while most others are still running. Maybe for a day the teachers have to get courses, ('studie dag' in the Netherlands) or for whatever other reason.