So, the kid carries
Or to put in a body of the toy truck of the favourite bear cub and to bring it, say, to kitchen.
Thus, in game the plot subject game develops.
In subject game the child easily replaces real object with another or in general assumes existence of the absent subject.
So, the kid carries a cube instead of the machine, imitating thus a motor sound, feeds mother with nonexistent porridge etc.
Accompanies independent game actions with emotionally expressive statements, a mimicry.
Has emotional satisfaction from actions with toys..