In a 3 year old child, most common cause of hepatitis is –
"Children usually acquire infection indirectly, through parenteral route from hepatitis B contaminated blood tran.sfilsion".
Other modes of transmission in children : -

Sharing of contaminated hypodermic needles used for multiple doses of infection.
Shaving razors.    •
Sexual contact Adolescent boy & girls.
Pin prick
Saliva exchange
Perinatal
Blood transfusion