This is an adaptation of the simple science experiment testing if objects are magnetic or not.
As my son is obsessed with Thomas the tank he loves this crane. He calls it banana cranky as it is kind of yellow and cranky is green from Thomas . He constantly attaches his trains and has progressed to be able to use the turning wheel about a month ago.
So I got the usual selection of objects
Put them in a cake tin
Wrote two signs saying magnetic and non-magnetic
Explained what to do and off he went.
Started off picking up trains.
Then he started investigating.