I am considering moving to Delft (or close by) for less than a year - I will have a position at TU Delft during that time. I have two children, a 12 year old (going into 7th grade) and a 4 year old. The international school in Delft does not offer a middle years program for the 12 year old, and it is quite pricey. Does anyone have an opinion of the local dutch schools like Grotius College for English speaking students? Will it be okay to send my children to public Dutch school for a while? What about the international school in the Hague?
The 4-year old should be fine and will probably pick up some Dutch easily (I have seen several do it) but I suspect it could be tougher for the 12-year old as schooling and school life are obviously in Dutch. I don't know anybody who did this but Grotius has something called an “Internationale schakelklas” which is intended precisely for older children who are alphabetized but don't know Dutch. It's mostly intended for kids who arrived recently to settle in the Netherlands and should therefore join the regular Dutch system (and not for expats who will move shortly to another system) but it could be an option.
There are many international schools in the Hague and you could certainly find one teaching in English and following your country's curriculum but they are likely to be pricey and to have a waiting list. Most pupils would be there for several years and have at least one parent working for an international organization (I think they get subsidies and priority on enrollment), I don't know anybody working at TU Delft for a short time who did this.
Less then a year is tough. As @Gala says for you 4 year old you are going to be okay. S/he will go to Group 1 or 2, which still could be considered pre-school. You might want to look for a school with a lot of bilingual children, so they could relate. My children (twins 5 yo) go to a school with a lot of bilingual children and it is fun to see how at their young age they enjoy counting in French, English and Polish.
For your twelve yo, things might be a bit more complicated, especially since you are only moving for less then a year. The american school in Wassenaar might be an option. Don't tell a Delft or Wassenaar native, but Delft and Wassenaar could easily be considered suburbs of the Hague. It could be a viable choice to live in the Haque, work in Delft and send your kids to school in Wassenaar.
According to the website of the Grotius college, they seem to cater foreign pupils, with a bilingual program. This is getting more and more common in the Netherlands, but it is certainly not the norm. So I expect that the Grotius college might be a good choice. Since television is not dubbed, but subtitled most 12 year olds in the Netherlands have decent knowledge of English. So the Grotius college might be a good choice for your 12 year old. Then again, you indicated that you will only stay for less then a year, the question then is if it is worth the effort. Your child would also need to get used to another school system, and in my opinion for only a year that is not worth it.
he went to the Rotterdam International Secondary School (RISS) in the end. We arrived in October. He had to wait until after winter break for a spot. We tried Grotius College but they didn't feel comfortable with the short duration. And my son has some learning problems (suspected ADD, but never confirmed). We stopped hearing from the after going for an interview. And we didn't have other options than RISS. My son loves RISS, though. It's a little expensive and a little far, but I think honestly it suits him better. The school is small and his current classmates are inclusive. He gets up before 7 to take a bus there. But it's the first school I've seen him like. So it worked out.