I’m often asked how we handle big kid stuff (legos, art supplies, open cups, etc.) with small kids around. It does require some management and there are times the older ones are inconvenienced.
We keep all small toys on the 2nd floor. Since mine share a room we have an extra bedroom. The little ones have no need to be up there without an adult. It is hard to convince one child to play away from people on their own at that age so they won’t get as much use as they would nearby or if there are multiple big kids. Art supplies are in a closet that only gets opened when babies/toddlers are napping. On rare occasions the younger ones are happy in the gated playroom and the older ones can use art supplies elsewhere.
(Can you tell we have boys?)
That being said, over the years I’ve found that some small toys are more manageable than others. For example, brand name Matchbox & Hot Wheels cars are not my first choice for toddler teeth, but they hold up very well unlike knockoffs so I have no knockoffs. Also, its easy to rush to the “big kid” toys. We have far more LEGOs than anyone actually needs and we didn’t even start with the oldest was well past 4 (youngest age on sets). My oldest gravitated back to the “baby toys” as soon as the twins got interesting enough to play with.