The concept of sharing is particularly difficult for your baby to grasp. It is unrealistic to expect your baby to give a toy to another baby if he is still playing with it. It is equally unfair to expect your baby to understand that he cannot take another baby’s toy simply because he wants it. What you can do is demonstrate the basics of give and take. Your child of 18 months is generally able to comprehend reciprocity, but you must demonstrate it in a way that is reasonable to him; if he takes another baby’s toy let him know that he must replace it with one of his own so that they can both play. Your baby is wholly capable of unselfishness and generosity, but any such act must be seen to be a pleasure for both parties. If your baby is willing to share his toys with other members of the family, encourage these small acts of generosity with others and try to build on them.
You should always include your baby in social gatherings and teach him the basic pleasantries from as early as possible. Introduce him to lots of new faces so he doesn’t become dependent on you and the family alone for social stimulation. It will help him feel secure when he is away from you or his usual caregiver, although this shouldn’t happen too frequently or for long periods of time.