Putting together a tool set for children 8-11
If I recall my time in the scouts well enough, I'd suggest the following:


a set of screw drivers
an 8-10oz hammer
a set of pliers
a small chunk from a bar of cheap soap for coating screw threads
a piece of chalk- both to use for marking things, but also to absorb moisture and prevent rust.
a small framing square
a retractable tape rule


If you shop around and hit discount stores, it's not an expensive proposition (in the US, I'd recommend Big Lots and Harbor Freight.)