From experience ... No matter how politely you say ,to others it will sound rude. Just say that they cannot touch or kiss because you don't want your baby to get sick as he or she isn't fully immune yet. Don't worry about what people think or say to you. What you're doing is for your baby's safety.
Speaking from experience banyak kali orang buruk kan kita for that. But it's okay I don't mind ,I don't get angry if they scolded or Hina or maki me Infront of my face😅 we can just pray Allah bless them with goodness in knowledge regarding this matter.