Hello,
My family (including 8 and 12 year old children at the time) really enjoyed the Escher Museum. The canals and city itself were also nicer than expected. Those two things alone are enough for me to recommend a day trip.
We would have been happy to spend more time there, but it was a long vacation in the Netherlands and we had already been to more art museums than my kids could reasonably handle...so can't comment on Mauristhuis unfortunately. We finished our day in Scheveningen. The kids loved the zipline and seeing the water, but I wouldn't say the carnival-like atmosphere is something i'd recommend. I was also interested in Madurodam (miniatures) and the Prison Gate Museum, but will have to wait for next time.
Cheers,