We went there for a weekend when dd1 was a baby and have been back on day trips from elsewhere in Normandy a few times since. We really like it. Big beach, great for running about and letting off steam. Not sure how old and what gender your kids are bp, but there's a big DDay museum, which might appeal if they are likely to be into tanks and such like. We've always had nice, unpretentious food at Le Perroquet on the main street... more upmarket cafe than posh restaurant ifkwim, but very relaxed and child friendly. (For posh nosh try the Hotel Le Marine. We stayed there, but didn't book into the restaurant when we booked the room and couldn't get a table.)
Bayeux is very nearby and worth a visit. My dds loved the tapestry last year (they were 3 and 5). Miss out the boring reconstruction upstairs, cut to the film which explains the story (there's an English version which they show at regular intervals through the day) and then see the 'real thing'. It is incredible. (OK - I admit to a slight bias, as I am obsessed with all things medieval, but it really is stunning.) Dd2 particularly liked the bit when Edward the Confessor dies and is shown laid out in state. She kept demanding to go back to 'the dead bit'!
There is a theme park type place within reach near Caen (just on the ring road) called Festyland. Haven't been there myself (tbh, avoided it like the plague) but would appeal to the kids!
The cheese factory at Isigny-s/-Mer is open to the public. We went round it on a wet day, and it was vaguely interesting... but only vaguely.
A bit further afield (heading up the Cotentin peninsula), Utah Beach is also gorgeous. There is a nice farm museum (very laid back, wander round in your own time - old implements, cider press, etc.) near Ste Mere Eglise (famous from the film 'The Longest Day').
If you're into horses, there's a famous stud near St Lo somewhere (haven't been, but wanted to and then didn't make it...) which does shows through the summer.
There's a good zoo-park (zoos are not my favourite things, but the animals have plenty of room to move around - no small cages) near Villedieu-les-Poeles, but that may be a bit far away. Ditto the excellent aquarium at Cherbourg.
I think some of the other beaches between Caen and Arromanches are nice too (e.g. Luc-s/-Mer and various other 'sur mers'! (We missed a ferry from Caen once, and went exploring up the coast road for a few hours, but it was March, so hardly beach weather. Very quiet then, but probably busier in the summer
I should be on commission from the blimmin' Normandy tourist board!