It's true that they have many many more children than christians, in average; but it's the same for the jewish community.
However, they still are a minority and live in the outskirts of large cities.
And we have a large immigration coming from Eastern Europe too (more recently) and had a very important immigration coming from Italy (in the 50's and 60's) Spain and Portugal.
As long as it is diverse, it's fine.
But we've had Kurds fighting against Turks in Brussels; is it just the beginning?
But even if there are serious problems to expect, all communities have spokpersons or religious authorities who can establish a dialogue with the communal authorities.
But we sure would like what's going on in the Middle East to end. It will end, that's for sure but when and how, that's the question.

Raoul