Despite the “Expert” opinions here I wouldn’t worry. How many adult thumb suckers do you see?
2 years old is nothing, perfectly natural. Shows he can comfort himself (ie look out for himself later in life maybe?)
All that overbite sh1te is a crock IMO, people with one would have developed that way anyway. It would take 24hr constant thumb-sucking for years to influence the developmement of the pallette. (see neck-stretching, lip-stretching, foot binding etc. for a reference)
I will stress I am no expert but did do some study on the burmese neck-stretchers and other body decoration/deformation during my degree. (jewellery, so like I said -no expert :?)
Let the boy develop naturally