English speaking rugby club for children...

Can I know to which rugby team you have been to and the age of your children ?

I know very well rugby in Belgium and I live similar experiences...

The only English speaking rugby club around. It trains at VUB in Brussels.
http://bbrfc-celtic.be/school/intro/

Well, not only, you have the british school that you could join also even thought, you are not from this school and you will find mainly English players. In the Bbrfc-Celtic, you would find English players but also many foreigners (Irish, Scottish, Argentinian, Australian, New Zealanders,...)
But also you have to take into consideration that the team of Asub Waterloo, even if they speak french mainly. The city of Waterloo is full of foreigners and thus in this team, you will find many nationalities and they will have respect for English players.

The British school rugby team is for children at the British school. They kicked out the players not at the school about 5 years ago and British Barbarians amalgamated with Celtic to form the single English speaking club. BSB no longer has a rugby club, only school teams.

Therefore there is a single english speaking rugby club.

Well, I know the trainer in BSB, and he told me that they are missing some players, I am sure he can accept English players to reinforce his team.

No BSB cannot accept non students. It became school policy, no more non students, not even staff children who attend local school are even allowed on campus, never mind in the teams any more. You need to go through a security audit to get on campus as someone who is not associated with BSB. Only Tervuren hockey club and British Scouts are still allowed on campus who are not students at the school and they are vetted before entering. It is sadly not possible.