Innocence and Child

Hannu is almost two years old and is using bottle for drinking milk. I thought its time for him to switch to cup and tried to make drink in a cup. All my efforts were vain. At last I hid his bottle and told him that ghost has taken away his bottle and he needs to use his cup for drinking. Listening to my words, my son has started trying out drinking in cup. He didn't even ask for his bottle once. But he is not showing much interest in having milk as he used to. His act made me feel guilty. By forcing him to take milk in a cup, am I lessening his interest in drinking milk? How innocent are kids. My son believes whatever I say. Am I doing justice to his belief? Earlier I felt bad but then I made up my mind saying whatever I am doing is for his sake and goodness.