I assume the sort of runners you're referring to are the original Blum design which everyone and their dog has copied over the years (some good, some awful, a lotbin between). This sort of thing, the Blum Standard Euro Drawer Runners:
The problem is that they are often only fitted using 2 or 3 screws per side, and those screws (from memory) are something like 3.5 x 16mm. So the limiiting factor is often the screws, although if needs be you can put 3 or 4 extra screws into the holes in the runners (there are quite a few holes in the sides to allowvthis), as well as going to longer screws, such as 3.5 x 30mm, where you have two cabinets adjoining or a cabinet sidewall with an 18mm decor panel on the outside. An alternative can be to use flat headed Euro screws
The best type were always the
original Blum ones, but they are getting scarcer these days, because they are relatively expensive (possibly discontinued?)
Fundamentally, though, they are all rated at about 20 to 25kg load per pair. TBH I'm surprised that your young uns didn't manage to wreck the drawers first, as they often gave very thin bottoms
But if (over)loading is the issue, another thing to go for might be ball bearing extension runners, like
these, which you find in a lot of office furniture.
Those are rated at 30kg a pair, but the same sort of design is available up to about 75kg/pair, or more (as used in mobile tool chests). The difficulty is that the heavier versions are often designed to work with a different style of drawer box which has a groove machined down the sides to accommodate the runners, so you might have to remake or at least revise your drawer boxes to accommodate them depending on the drawer runner set chosen
BTW what sort of damage are your kids actually doing?
