We have these in our home.... the Habitat Tam Tam Plastic Stool. It's lightweight but not flimsy and the kids use them as bongos. Get yours from Argos Outlet at eBay. They are just £11.25 with FREE delivery and are a fun piece of furniture for any room in the house but especially children's bedrooms.
I am not the only one to have these, my friend bought these for at her breakfast bar. We use ours, or rather our boys do for playing on their XBox. They are just ideal for that purpose. Another way of using them is for sitting outside one the better weather is here.
These are full size stools and are really not suitable for little children. Mine are aged six and nine years old, they use them fine. They like that they can store Lego inside them too. These can be used as stackable storage when taken apart.
Remember delivery is completely FREE or you can collect from your local Argos should this be more convenient.