There are some great rafting places up north that are a lot of fun- I like Kfar Blum.
There’s also the Hula Valley, where you can rent bikes and bike around the lake.
Also Tzuk Menara (which I’m pretty sure is next to Kiryat Shmone), which has a gorgeous cable car ride and Alpine slide. (Do this instead of Har Chermon- just as pretty [though in a different way] and much less out of the way.)
In addition to the mekomos hakedoshim in Tzfat, just getting lost in the old city can be a lot of fun (though perhaps not with little kids…).
There are banana boating places on the shore of the Kinneret.
Lots of great hikes in the area- if your kids are old enough and nobody is afraid of heights, the Arbel is a lot of fun.
If you’re interested in hiking and archaeology, Gamla in the Golan is extremely cool. In fact, there are amazing archaeological digs all over the place up north- Katzrin mishnaic village, ancient shuls all over…
(Can you tell I just came back from seminary? 🙂
I wanna go home!)
Just saying- if you’re in Yerushalayim and have a car (though it is accessible by public transportation), do the Temple Mount Sifting Project. Very cheap (10 NIS for two hours) and really, really amazing.