Does Islam don’t support and adoption at all if we adopt baby from the day baby is born. can baby girl be adopted while having a real daughter is this allowed cause it will be a baby girl not bay boy?
This is allowed whether it is a boy or a girl. The problem is the same. The boy is not a mahram for your daughter or you. The girl is not a mahram for your husband, your brother or your son.
Unless one of the family suckles the child when it is below 2 years of age, it is not mahram to the opposite sex.