There are no border checks between Eire and NI, however I'm doubtful if it'd be legal to go between them without it. I'm sure it's very common though.
So CAN you? - Yes.
Are you allowed? - Probably not.
Yes, anyone from Northern Ireland or Ireland can get an Irish Passport.
Yes, a baby can travel domestically within the United States without a passport.
No, a baby cannot travel without a passport. All travelers, regardless of age, need a valid passport to travel internationally.
No, a baby cannot fly without a passport. All passengers, regardless of age, need a valid passport to travel internationally by air.
No, you cannot take your baby to Mexico without a passport. All travelers, including infants, need a valid passport to enter Mexico.
No, a baby cannot travel to Canada without a passport. All travelers, regardless of age, need a valid passport to enter Canada.
No, a baby cannot travel to Mexico without a passport. All travelers, regardless of age, are required to have a valid passport when entering Mexico.
No, a baby cannot travel internationally without a passport. All travelers, regardless of age, need a valid passport to enter another country.
No, your baby can't. Nobody can travel without a passport, and it makes no difference how old he is, or the destination.
No, babies need a passport to travel internationally, regardless of their age.
If you need a passport there, the baby will also need a passport. Maybe there is the possibility to get your baby written into your passport.
Surely this is a joke? News for you, its not funny.