Fairmont Hot Springs?
 

No, not the castle... the small town on BC side.. as i was scrolling through the map looking for potentially interesting and not overdeveloped tourist traps this one popped up as possibly appealing..

Any feedback from those who visited either in summer or winter?

I am looking for smth practical with kids eg large pool, activities (hike, bike, ziplines, tubing, ski/xcountry etc etc) with nice nature around. Typically we go from lax for 2-4 days so reasonable proximity to airport is important.

I've only driven through.Not sure it's even developed to the degree you're hoping for re: kid activities (zip lines, tubing, etc.) Just the traditional (presumably winter) activities. It is a very small town.

Not too many airports around. Nearest major one of course is Calgary/YYC and it could be challenging in winter to get there (road isn't particularly treacherous but it's still winter). Smaller, nearer airport would be Cranbrook (with commensurate small plane service). I didn't even know Fairmont had an airport or air service. Don;t even think about Castlegar as it is further away, requires travelling on the Salmo-Creston highway and is often socked in.

formerly Radium Hot Springs
 

We have been twice - back in the day when it was known as Radium Hot Springs. It used to be a place where you went after a day of skiing/mountain biking/hiking etc. Now it been spruced up to be a destination in and of itself (see https://globalnews.ca/video/5488207/...rt-renovations).

I haven't seen the renos so I can't say how well the zip line works! My advice? Plan to spend 2 hour and bring along towels, a lock, flip flops and snacks for the kids. All of these cost extra (of course). For our last visit (2017) parking was free. Hopefully that has not changed?

You should note that Radium Hot Springs and Fairmont Hot Springs are two different places. With the former being about 35 K north of the later.
For the original poster try a Google search of what to do in Fairmont Hot Springs. You will fine there is quite a variety of things to do.