My LO has the tendency to suck his thumb together with a piece of cloth (e.g. his shirt, handkerchief etc). How do I stop him from doing so?

Reckon it is self soothing for him to do so. A teething toy would be a great distraction. It will give him something to play with and it will satisfy baby's need to chew or bite on something when he feels the need to self soothe :)

Maybe give him something that will make him be busy with his hands? Like a toy, or something that he will be actively playing with? :D