"This pretty child had become the army mascot"

Creative Commons Attribution Share AlikeCaligula - Credit: Ed Uthman
The reference here is to Claudius's young nephew, Gaius, the son of his brother, Germanicus. Gaius, who succeeded Tiberius as Emperor, is more commonly known as "Caligula", meaning "little boots", a nickname he acquired as a child on his father's campaigns.

This anecdote, together with the account of the mutiny of the troops in Germany, is elaborated by Graves on the basis of Suetonius's account of these events.