Yes that's what I thought. Here it's 6 and 4 although we don't call 4 pre-school. At least not anymore. It's called group 1 these days. Going to school from age 5 is obligatory but many people opt for 4 since it's possible.
Copied from wiki:
Until 1985, it used to be a separate non-compulsory form of education (for children aged 4–6 years), after which children (aged 6–12 years) attended the primary school (lagere school). After 1985, both forms were integrated into one, called basisonderwijs (Dutch for primary education). The country also offers both private and subsidized daycares, which are non compulsory, but nevertheless very popular.