Hi again,
you seem quite decided on a bilingual school, so thought I might just add a little bit more about the 4 bilingual schools in Brussels (ok one is a few metres literally outside). They differ quite a bit in their intake and also in their philosophy.
Ecole Acacia
www.ecoleacacia.be/
This is in the heart of Etterbeek, 10 minute walk from the Berlaymont (central point for EU district). It´s a fairly new school opened in 2002. It follows Belgian school years and uses its own teaching methods and in primaire teaches a modified Belgian curriculum. It is fairly Catholic but there will be pelty of non Catholic children, the attraction for the parents is the bilngual education rather than the religion. It has 2 streams for maternelle, an English/French one and a French/Dutch one. The school took over an empty local school and the building has been refurbished. I would expect there to be a majority of French speakers first language here, but apparently expat English speaking children too, a bit like Ecole le Verseau in Bierges, plus some Dutch first language but wouldn´t think there are many. It used IMMERSSION method in that there is ONE TEACHER, ONE LANGUAGE at a time, the timetable is divided into French or English, but not mixed, unlike the Montessori schools.
I have been told by parents who have done the open day tours that the maximum fees is around 5K per year. Age 1 1/2 to 12.
Brussels International Catholic School
www.bicschool.be/
Again in the heart of Etterbeek, about 15 minutes walk from Berlaymont, this is also a farily new school, the maternelle was refurbished last year and the primaire/secondaire apparently over the summer. This school is much more Catholic in primaire/secondaire years than Acacia, a friend had no problems with her child in maternelle with the religious side but in primaire it may not be suitable for a family who is not of the same persuasion. It uses IMMERSION like Acacia with the timetable divided acording to language. I´ve been told it is roughly 50/50 between French and English speaking families here. Fees are 5.6K per year. Age 2 1/2 to 18.
Montessori House Brussels
www.montessoribrussels.org/
This school only opened in 2006 and has 2 classes, 2-4 and 4-6. The owner has another school in Braine. There must be no more than 50 children in the whole school, although the classes are big´like International Montessori, it´s because there are 2 teachers for each class, one English and one French, I´m sure they must sometimes take advantage by separating the children into 2 groups. The school is jsut off Montgomery roundabout in WSP, great location as it´s only 2 metro stops to Berlaymont. The 2 to 4s can go part time. Children mainly from expat backgrounds, varying languages. Fees from 6K to 10K.
International Montessori Woluwe
www.international-montessori.org
This school is metres outside Brussels (WSL) and easily accessible by bus to Berlaymont or bus/metro. It opened in 2008, it is an exceptionally beautiful converted cloisters on the edge of countryside, has gradually grown in size and should have children aged 2 to 12 there with perhaps over 100 children as it is adding over 8s in September. Like the other Montessori, there are 2 teachers per class, so classes are over 20 each. Children mainly from expat backgrounds af varying nationalities with many English speakers, not many French speakers. 2-6s can go part time. Fees from 8K to 14K if paying yourself.
I´ve written the fees in case you wish to consider the younger one staying with her elder sibling.
Hope the additional information helps.
Good luck