You can use Vicks on a baby as long as they are 2 years old or above.
If your baby is under 2 years old you should never use any Vicks on your baby either on their feet, chest etc as it could harm the baby.
The Vicks can make it harder for the baby to breathe and could cause death so do not use Vicks on the baby under 2 years old but if the baby is 2 years or above Vicks can be used on the baby to help them breathe.
They make decongestants for babies under 2 so you should use those so you don't risk harming your baby.
Also use a humidifier in your babies room if they are congested or has a cold etc and that moisture in the air can help the baby to breathe.