Hi there
with an 18 month old, your child would only be one year away from being able to go to full/part time free maternelle (French) / kleuterschool (Dutch). Would you be looking for a 3 day a week creche / kribbe for work purposes or just for a break? I am asking this because there is a system of drop-off creches here which are reasonably cheap, some can be booked in advance, some literally turn-up at 9am and hope you have a place for the day. They are either called 1) haltes-garderie / haltes-acceuil and there is usually one in every commune and are for all day care, or 2) the Farandoline system (some have a different name to this) with half day care, a permanent member of staff and parents go on a rota to help with child care. I am not entirely 100% on costs, but estimate that you are looking at less than 25 euro per day for this type of care, possibly less. The other system is traditional creches. They fall into 4 categories : 1) the public creche system, virtually no chance of a place unless both parents are working and reservation is made before 4 months pregnant, priority to those on a low income too, 2) private creches which are inspected either by ONE or Kind en Gezin, typically cost 450-600 euro in Brussels, again reserve mainly full time places before 4 months pregnant, 3) private creches which are inspectec by ONE or Kind en Gezin and which market particularly to expats eg KidsFarWest and Kids Attitude which have about 10 creches in the east Brussels areas, these ALWAYS have vacancies, a full time place costs around 800 euro per month, a part time place costs 50% more pro-rata, many many expat children there on part time contracts, they are willing to give short term contracts 4) private creches which are NOT inspected at all and the only ones which are not tax deductable, not too many of these eg Thumberlinas.
You could try and secure a place at one of the International Montessori group schools in east Brussels / Vlaams Brabant, but for 3 days again you are looking at 850 euro per month, term time only at least, unlike all the other creches which are open 51 weeks of the year.They take children at some of the schools from 15 months old. International Montessori are nominally French / English but in reality these are minority languages of the children, don't expect too much French being picked up there.
No it should not be any or much more traumatic going into French than going to a new setting for a child that age.
If you do move and are interested in maternelle / kleuterschool, do look immediately for a place, the most popular schools will do their enrolments 18 months in advance.