Check out Flathead Lake.
I liked Polson.
whitefish is great to spend a day, day and a half in.
I didn’t do much of the rest of the state. On one of my trips we came through Yellowstone as well. Had dinner in Bozeman but that was all we had time for there.
The itinerary I mapped out for us between Yellowstone and Whitefish/Columbia Falls had us spending the night in Butte (this was just my girlfriend and I, so sans kids). I wouldn’t exactly recommend that, but we did check out the superfund site which was really interesting (to me at least).
I’ll look back at the hikes we liked.
I recall Avalanche Lake which is on the main road just before you start the climb on the GTSR road (ask your 7/8 yo to figure out why some of the trees that are down fell “uphill”) . and then at the top/Logan’s Pass, Hidden Lake is super easy and fun for seeing wildlife (marmots and mountain goats, mostly). And going the other way, try some of the Highline.
Many Glacier has some beautiful hikes as well, but that part of the park is also a haul to get to and I think the ones I did there were a hit more challenging (may have just been my girlfriend and I), but Iceberg Lake is one I remember that was excellent and may be doable since it sounds like your 7 yo is not like mine and tolerates hikes well.
North Fork/Bowman Lake, make sure to bring bug spray (same for avalanche lake). There is a nice easy hike along the lakeshore to give you different views of the lake. You can branch off and start climbing towards Numa Fire Lookout (but going all the way was one of the harder/longer hikes I did). Views were incredible but definitely not one for the whole family.
If I think of more, I’ll post
And damn I miss Glacier. Not in the cards this year, but definitely want to get back sooner than later. Would LOVE to find a second home up there…or even just a plot to building something on in the future… but poking around and looking at prices a few months ago, that’s a big nope.