Why don't you try getting your toddler to drink the milk whilst you read a story and then when you leave the room it's lights out with no distraction. If he/she has not finished the milk by the time you have read the story then it is obviously not needed and is removed when you leave.
I totally agree with Ellie on this one. Your son is really young so there is a chance this can be nipped in the bud. My son is 4 this month and once he's in bed all he does is call after me and his dad. We give him a kiss and a cuddle and that's it. After about 5 minutes of calling us he gets fed up and goes to sleep.
