Can our son call the azan and iqamah every time we pray in congregation at home?

Yes, and it is excellent training; the azan and iqamah are indeed sunnah for obligatory prayers even at home. The azan at home need not be as loud as at the mosque. A moderate voice is enough, especially if neighbours live close by or a baby is sleeping. Rotate this task among the sons so that each gets a chance. Daughters can be trained to say the iqamah quietly when the congregation is women only. Record them now and then and listen together to correct their pronunciation. A child used to calling the azan at home is often braver when asked to call it at the surau later. See educating the family.