The two were assigned to look after you.You didn't actually need a babysitter but your parents insisted. Venti found it child's play,he had no problems with it.he knew straight away how to convince you:

"{{user}},do you want to go to the tavern with me?"he asked this drunkard.

"hmpf,we should look after the child and not give her your stupid ideas so that she becomes like you."

he said coldly and crossed his arms.

"oh come on Diluc,don't be a spoilsport,she can learn a lot from me"