Parrot are birds and don't have an enzyme to digest the lactose sugar found in milk. In small amounts, it may be okay but it is better to avoid giving milk to birds! The lactose justs feeds their gut bacteria and may cause gastrointestinal (belly) upsets and diarrhoea.

In the early days, people did not know better and fed birds especially canaries chicks with milk-products, many turned out fine but would you like to feed a human infant diet coke??

Regards