I recommend Interhouse for renting an appartment/house.
The staff has been very helpful and nice to us. In all issues we came across during our rental period they were able to support us very quickly and nicely. they are very understanding and reasonable people and as an expat who has just relocated to the Netherlands with a small child thats exaclty what you need. Highly recommended.
More from our blog:

Temporarily letting a property meant for your studying child, this is how it works afer July 1st 2024
When Will and Lilian heard their daughter Sophie was accepted at Leiden University, they couldn't wait to celebrate!
Read more

Temporary letting through the Vacancy Act: how to avoid vacancy and high costs
Jack always loved living in his ‘tiny house’. But when he fell back in love with his childhood-sweetheart after 40 years, it turned out that she ...
Read more