Clingy toddler

[josieanne91]

My son is 21 months old and is over bearingly clingy. To the point where we can visit the grandparents house which he knows very very well, yet if I'm there, he will scream blue murder if I put him down or if anyone else tries to play/cuddle him etc.
In our home, he's clingy but will go off and play. As lovely as it is that he wants to be with me, it's becoming difficult that others are now noticing how he doesn't want to interact with them while I am there and is acting very shy. What can I do to encourage him that going off and playing with others is ok and that mummy will still be there when he needs reassurance.