Any tips for Duinrell (including how long to go for)?

[HiDBandSIL]

I'm going to book it this weekend. We're a family of 4 with a 3yo and a 1.5yo.

Should we go for a week or two of something in between?
If less than 2 weeks, where could we go for the second stop - Efteling?
Recommendations for day trips?
Can you hire a bike trailer (to carry children in!)?
General tips / things to do / take?

Forgot to say: going in the summer, early July

A week is good. I wouldn't do 2 weeks myself. There is lots to do and if the weather is nice, you can spend time at the beach. We loved it there.

Scheveningen is worth a trip, maybe Amsterdam if you are feeling adventurous. We took bikes and did loads of cycling.