Hi Richie,
This will be our 3rd time in Duinrell 22-26 aug then off to the Dam for 3nts(me,Mrs and 9yr old son) it's a fantastic place, the kids will have a blast especially as they are a bit older, ALL the rides are free, the swimming costs next to nothing for water slides etc, and like max said locally the area is beautiful, the bike rental on site is cheap and the bikes are all in great condition can even hire (speed limited) mopeds if your not feeling the bike vibe so you should'nt have any bother, food shopping wise there is a great shop called Jumbo in Wassenaar just cross the road from the main entrance 15min walk and personally chance for my morning wake and Bake. There are also some great little restaurants along the main street and nearby, everything is close by but again like Max said it's an absolute desert in regard to CS's.
Now onto the important bit

the nearest coffeshops are in Leiden (10k) there are 4 I personally use all clustered around the town centre/square 2 run by same gang (try the Mr bubble if they have it, I'm a heavy med user and it made me wobble) now this is MOST important they don't open until 17:00 and YOU WILL BE ASKED FOR PROOF OF AGE (I'm 45 but look even older and I got asked first time just lucky I still had my passport on me) and they Absolutely stick to the 5grm per day rule, but if you do all 4 should last the week that's what I usually do and still have a little left for a nice reminder when I get home
Sorry for rambling on hope you and your family have a great time, if you happen to see a chap with a dark dragon shaped walking stick (usually) wearing a green floppy hat or a black st pauli baseball cap and crocs it's me, always happy to meet a fellow acd'r and burn one down,but no problem if you just want to crack on
Keep safe whatever you do
H