If you're familiar with the area around Ecole no7 and have chosen it because you're happy, I'm sure you'll be fine there.
It wouldn't be my first choice of area, simply because I am so fussy and like the swimming pool within walking distance and running track, there is in fact the Ixelles sports centre and American gym in that area which has activities for children, plus a private and reasonably priced pool (Archimede) as well as VUB pool and sports centre. You just won't find as many expats as in the Woluwes and there can be much advantages to it being a student area with ULB and VUB there!
Just do your homework as above, though I'm sure you already have done.
Ecoles 7 and 8 are next door to each other. The nearest public transport is tram 25 which goes directly to gare d'Etterbeek. There is also trams 7 and 94 which you could use to get to work / home, I'd definitely live near a tram stop for 7, 25 or 94 and as near to school as possible, yes that might also mean a Watermael-Boitsfort 1170 or Etterbeek 1040 house/flat as well as Ixelles 1050. the 7, 25 and 94 trams are all fast ones as they run mainly on their own lines, except through the ULB area where they share the road. They are certaininly quicker than buses and driving. there is even perhaps the option of Watermael to Etterbeek by train?
It's not going to be easy to avoid General Jacques as gare d'Etterbeek is on it! But a car will be a liability, I cannot stress enough the use of the tram in that area or bike if brave.
If you want somewhere quieter and more suburban, then you'd have to look at the Woluwes which are quite quick by tram in fact and become more suburban the further east you are from Montgomery roundabout. Or going southwards on tram 94 brings you to Boitsfort part of Watermael-Boitsfort. there is la Futaie/les Coccinelles schools and Assomption along that route next to tram stops, the former is usually quite easy to find a spot at, Watermael-Boitsfort is not so pressured for population growth so school places are easier to find except at the most popular schools like St Hubert and la Sainte Famille. Les Cedres / La Roseraie schools are also on the 95 bus route, I'm sure that bus is not too slow and it does again go directly to gare d'Etterbeek and these schools have usually a greater number of expats which makes getting extra help with French easier - extra help in francophone schools is now available at primaire level if the school has enough non francophones AND it uses the money allocated for that purpose! It varies from school to school and head count done each year I believe for this purpose now. No idea how many non francophones ecole no7 has, but I'd ask the school, it could be quite high due to the students living in the area and large international contingent.
www.stib-mivb.be/netplan-plan-reseau.html?l=fr
You've done well to get school places, If you're happy with the area you've chosen and can afford housing in budget, you may just have managed hopefully a good choice. Further north in Ixelles the schooling situation is much much different and in fact parking is far harder up there too.
Please please come and join our Benelux mumsnetter page if you want more advice, or the other FB groups, loads of advice there.