Hi there,
welcome (soon) to Belgium, hope you find the place as great as we do.
I can only echo what Portofino has already written, AVOID if possible the R0 or E411, Hoeillart is therefore not really a good place to live if commuting by car to Zaventem, house prices are also inflated by the high number of expats there who send their children to BSB, St Paul´s, ISB, the international schools in the south and east areas in and around Brussels.
Don´t worry about dance lessons, children´s activities are plentiful and cheap, you´ll find dancing courses all over the place.
You are looking for a welcoming school too, that may be a bit more difficult to get spot on, people choose schools very much word of mouth and reputation in the greater community, you do not have this luxury as outsiders to be able to tap into locals and their opinions so quickly or easily. Unless you are fixed on a certain area or school, at the moment with the excess of rental housing and rental prices going down, perhaps it would be wise to find a house first and school second.
You also would like a good easy commute to Zaventem, small community, tight budget. Here is what the communes/gemmenten around Zaventem offer in these respects :
Woluwe St Pierre (1150), Kraainem (1950), Wezembeek-Oppem (1970), all French speaking majority, some fantastic schools, some well chosen spots in these communes would fit the "small community" criteria, depending on where exactly in Zaventem you are going to, you could avoid the R0, but one BIG BUT and that is that you will struggle to find a 3 bed house for less than 1300 euro per month, it is one of the most desirable areas to live in the Brussels area.
Tervuren (3080)including the villages of Duisburg, Vossem and Moorsel and Bertem (3060) including Leefdaal (3061), Dutch speaking, some reasonably rural areas, some cheaper housing than the communes mentioned above except the areas closest to the British School, again great local Dutch schools, but you can get all you are looking for closer to Zaventem.
Kortenerg (3070) including Erps-Kwerps (3071) and Everberg and Meerbeek (3078), Stenokkerzel including and Melsbroek and Perk (all 1820), Kampenhout (1910) all a good commute and you can avoid the R0, generally a bit cheaper than the above Dutch areas, again good Dutch schools.
Zaventem (1930) including the villlages of Nossegem (also 1930), Sterrebeek (1933) ans St Stevens Woluwe (1932). Zaventem centre is more of a town, the other parts of the gemeente are more rural, Dutch, easiest commut of all the areas, great schools, can avoid R0, I really think either this area or Kortenberg etc fit your criteria best. Sterrebeek is probably the most expensive part of Zaventem, as it borders Tervuren and Wezembeek-Oppem, but in the south side of the village, access to Brussels is even possible by tram, yet you are also in the countryside. You should be able to find a 3 bed house here for 1000 euro per month.
I hav given the post codes as you might find searching the Immoweb website easier if you have them to hand. You can also use www.vlan.be and choose a central pojnt and limit your search by 5 or 1Ã kms for example.
Hope all this helps.