Once he's found the words to describe his fears, reassurances from you will help quell them. And make sure you give your child equal amounts of attention when he's feeling cheerful and confident, so that you're not unwittingly encouraging him to act fearful. If your toddler gets timid when he encounters new people or enters new places, help dispel his fears ahead of time. When you're heading out to a birthday party or playgroup, for instance, name the people he'll know there and mention the new ones he might meet. Take it slow.
Transitions are difficult for everyone, but especially for young children.
Rather than thrusting your toddler into a strange environment or letting an unfamiliar person get right in his face, try the slow approach. If he freezes up when you plop him down in the sandbox, for instance, climb in with him and let him sift and scoop from the safety of your lap. Teach your toddler how to tolerate your absences with a little role-playing. When he's rested and in a playful mood, set a kitchen timer for one minute and exit the room. As his confidence grows, slowly lengthen the time you're apart.