Before I explain to my child, I must first know whether the child can think and talk about bitcoin or digital money. If it is ready to talk, I will explain and I introduce to the child according to the portion. I will not teach bitcoin or digital money if he can not think in mature.
Not all kind for children show interest so if you did not find him interested just try to make him get involved in bitcoin so in future he will start loving it when bitcoin will give him money to buy things. At first try to teach your child at level where he can understand easily then tell him about bitcoin, show him any bitcoin video and internet link so he will know bitcoin and start using it for small to large level.