I think it's partly a question of how old your kids are, their physical strength, their size, etc. CO2 guns are pricey to feed, and tend to be a bit problematic in my experiences with them. (I've owned a dozen or so over the years) Their performance suffers badly under about 15C too, so warm-weather shooters...when they're running right. If you choose a spring-piston air rifle (break-barrel)...they're MUCH better, but many are very difficult to cock, and are adult-sized. They all break-in with time and get smoother. That Slavia is a very good choice, I just personally bought a springer myself, a Diana 24 in .22. Spring piston guns are considered the lowest-maintenance, but do require you use the proper scope if you're going the optics route. All scopes are built with rearward recoil in mind, but since the piston actually fires forward...the recoil is in the opposite direction initially. It can rattle even a good scope loose (internally). Airgun scopes are designed with this in mind, and protect against recoil in both directions. Should be said, these are also the most quiet air guns you can buy in Canada. The sound of the pellet hitting the target is usually louder than the gun's "report" itself.
A decent compromise is one of the pump-up, pneumatic air guns Crosman makes. Even for young, small-frame shooters...they can usually muster 5 pumps or so. These function from about 4 pumps up to 10 normally, but any more than 10 gives no extra velocity..but does risk damage to the gun. One I own might be perfect, it's a 1377 pistol with a 1399 "carbine" stock. Very light, easy to pump, single shot, etc. Pneumatic/pump-up air guns (like CO2) go off with a distinctive "crack" sound, but unlike springers...there is no recoil of any kind=any scope will work, and not suffer.
There are several online airgun retailers, the one I've done the most with is D&L airgun in BC. Even if you don't buy there, their site is the most comprehensive. AirgunSource (
https://www.airgunsource.ca/en/) here in Ontario is also highly regarded, and lots of Crosman offerings.
My kids learned on slingshots, then Daisy BB guns (they bored of those easily)..then a CO2 powered single shot rifle, then a Savage Rascal. The Rascal was by FAR the biggest hit, and even though they've all out-grown it..they won't "let" me sell it. tiny thing. Part of the fun there is the low-power, CB Long and CCI "Quiet" 22 ammo. Ours is scoped, wears a bipod...and even when young, the kids could blast clay pigeons at 50 yards...and even pick-off the tiny pcs. reliably as they whittled them down. Good times!