Comfrey is a bit controversial internally. I use it often that way but would be more cautious with a child.
Fortunately there are some other great vulnerary* herbs that can be taken internally without concern.
Gotu Kola (nearly as good as comfrey)
Plantain
Calendula
Gumweed
Rehmannia is also very good for bone healing and is much more yummy than the others.
Doc
*Vulnerary=accelerates cell division and tissue healing
Don't use herbs or combine herbs with medications or use them during lactation or pregnancy without talking with your healthcare provider.