Let the child fill the boxes with small toys and drag the train across the floor.
Does the child drag the train spontaneously, without coaching from you?
How far does she drag it?
Does she fill and empty the compartments?
Also offer the lids to the boxes so the child can cover up what is in the compartments.
Chant "choo, choo" as the child drags the train.
A more permanent version could be made with plastic shoeboxes.
The child will walk along to pull the train and will see how pulling something can make it come closer.