When a remaining battery power amount of a child appliance is lowered, a battery recharging operation of the child appliance is not quickly carried out, lowering of the remaining battery power amount of the child appliance is displayed on a mother appliance which is owned by a mother. When there is a risk that the remaining battery power amount of the child appliance is lowered and thus operations of the child appliance will be brought into a malfunction condition, a content of a special instruction is stored into a non-volatile memory employed in the child appliance. Otherwise, while the content of the special instruction has been stored in a management server, an operation may be carried out in response to the instructed response after the remaining battery power amount has been recovered to a sufficiently high battery power amount.