Good day! Do you give your children water after breastfeeding? I read …

Good day! Do you give your children water after breastfeeding? I read that babies under six months shouldn't have anything besides milk. But my mother-in-law says they need it, otherwise there will be constipation in the baby. I don't know what to do, who to believe. We're exactly ten days old today, I think it's too early all the same?