Children integration in a new school in the Netherlands

Hello

By children I assume you're talking about age 5-13 which is basisschool (elementary) age
Assuming both or one of the parents are working
Assuming English is your children primary or second language at the moment.

Constraint (almost certain) conditions:
-Private school / bilingual school is expensive
-Basisschool is basically subsidize by the municipality – cost around 100-200 EUR per year (even this is if you don't pick up your children during lunch time, if they goes home it can be cheaper).
-School in 08.15-08.30; school out 15.00
-Age 5 is group 1; age 6 is group 2 and so on
-Until group 4 or maybe 5, it is almost mandatory for parent(s)/custodians to bring children to school and to pick them up (one alternative if one cannot pick up at 15.00 then enroll to Buitenschoolse opvang (BSO) and they will pick up the children for you for another activities until your office hour).
-All will be done in Dutch/Netherlands language, and the language challenge will be significant exponentially starting group 4. As the children start to write in proper manner and some complex vocabulary are introduced.
-In the cities, all postcode have their own basisschool. And it is compulsory for registered children within the same postcode with the basisschool to be prioritized for enrollment. If it happens to be one of favorite school in town, one may find this as an advantage shall the ‘school' is within the same neighborhood.
-Kids choose whom they want to play with (for birthday party, play outside, etc.) in front of other kids who were not ‘invited'. If your family is not used to assertiveness, be prepare for this.
-Cannot skip school. Maybe 10 days per year is allowed but with a very good reason.

Given above condition, it would be ideal if the school is 5 minutes walking from your house or the same path to your office. I personally feel fortunate my daughter enrollment was at group 1. Even when she's a bit struggling with the language school advise to go to logopedie (speech therapy) without have to sacrifice her level. I've heard from some parents that their children have to stay one year longer just to adjust the language, especially for older than 10 years old.
Group 4 or higher, teacher will not segregate how to convey subject (in Dutch) towards children (regardless their background/capability). Therefore if your children start their new life at this level or higher, you may want to consider extra  effort (another course after school, mingle with other parents/kids, etc.)

Keep good communication with teacher and school, and see the discrepancy (if there is any) between teachers account in comparison with your children's story.

Success,
Regards,
Danlap