Whats the longterm health implications for a child born with an extra digit on both hands?

Depends on variables. Most extra digits are poorly formed&attached by a thin stalk.These are often removed @ birth with no consequence.Occasionally we see completely formed extra fingers, usually on the pinky side & these are usually left alone. Other than being a curiosity, they function as normal fingers.The genetics are usually autosomal dominant but can skip several generations & express differently when seen.