It happened just after 16:00 GMT on the Toberdoney Road, in Liscolman, near Bushmills.
The boy was taken to the Causeway Hospital before being transferred to the Royal Victoria Hospital in Belfast.
A man in his 70s has been arrested. Police have appealed for witnesses to contact them.
A nine-year-old boy has been critically injured after he was knocked down in County Antrim on Tuesday afternoon.