The son and heir of Charles I is shown as an infant on 30 January 1649. At this time, the prince (who later became Charles II, Restoration King) was in his late teens and had two younger brothers and three younger sisters.
The baby is an obvious doll.
Oliver Cromwell tells King Charles I that he has become Lord Protector. Cromwell did not receive this title until 1653, while King Charles was executed in 1649.
Blackadder exclaims, "One measly civil war in the entire history of England and I'm on the wrong bloody side!" He is forgetting all the civil wars of the Middle Ages.