Check out the historic "The Grove" nature preserve in glenview, as well as Wagner Farm (for the real young ones)..... check the glenview park district website for more details.... also, near The Grove is the River Trails Nature Center.... all 3 of these are within 15 minutes of the mentioned Kohl's Children's Museum....
I would definitely recommend the beach---every kid loves the beach! HOWEVER, forget glencoe beach....for a family of 7, it will cost you dearly to visit for the day (illinois is pitiful when it comes to water access rights, but i digress)... a MUCH better, and FREE option is gillson beach in wilmette..... try to go during the week---FREE street parking is impossible on the weekends, unless you get there real early..... the caveat is they don't allow swimming in the FREE area....you can get a daily beach pass and go to the swimming beach, but again, it will cost you dearly---and once again, our archaic water access laws are pathetic.... you can get around these access fees by either getting to the beach very early (impossible with kids), OR, in the evening, just before sunset.... there's something to be said about an evening outing at the beach....
Other activities and attractions in the northern suburbs:
The pretty huge car show on monday nights at westfield old orchard mall in skokie (the OUTDOOR mall is pretty nice in its own right....the show typically attracts 200+ vintage cars), downtown evanston (nice strolls along the lakeshore, plus a lot of resto's and stuff to do), lighthouse beach in evanston (gorgeous beach to go to in the evenings, plus the lighthouse is active---you can tour it on the weekends), ravinia festival in highland park (beautiful outdoor music venue--sometimes they have kids shows), downtown highwood (lots of resto's....plus you're close to the openlands nature preserve).... you can also google the various FREE concert and movie nights in the various nearby suburbs.....