Valerian II was the eldest son of Gallienus. He was given the rank of Caesar at the time of his father’s elevation to the throne but died about two years later. This antoninianus dates to the period of Valerian II being Caesar ie AD 253-255.
The obverse of the coin shows Valerian II facing right with the legend VALERIANVS CAES.
The reverse shows an infant Jupiter seated facing on the Amalthaean goat walking right. It is RIC 3.