My 20 month old just starts crying when relatives try and get friendly with her, she doesnt play with other kids too,likes to do her own bit..how can i make her more social?

My nephew is about 1.5 years old and is the shy-est little being I've ever met. Everytime he comes over to my place, he literally walks with his head down, hands pulling his mummy's skirt and walks so close to his mum, I thought he'll trip her over. Kids have their own characteristics too and some may take a little longer to warm up to people whom he doesn't met frequently. Bring him often to the playground or parks where he can mingle with other kids. Or join a baby gym where he might feel a little more comfortable with kids his age. Take one step at a time :)