Answer:One year old
Explanation:A one year old begins to recognise, get attached and become affectionate towards their care-givers however they are at the stage where they are aware of someone they do not know and they are usual not comfortable with those strangers.
The reason why they cry when they are dropped at the day care centre because they start to experience separation anxiety; where they don't want to be separated from the familiar faces or from those with whom they already feel comfortable.
