Sucking is a completely natural behaviour for children, as babies are born with a reflex to suck any object placed in their mouth. In their first few months, this helps them establish feeding, but thumb sucking is seen more as a self-soothing behaviour. While the issue often resolves itself, this isn’t always the case.
If thumb sucking continues past the age of four, this can cause implications such as protrusive upper front teeth, tipped back lower front teeth, an open bite where the upper and lower front teeth do not meet or a crossbite where the formation of the upper jaw is too narrow.
For these issues, orthodontic intervention is often required in the form of a thumb crib appliance or braces.
However, you can help them stop this behaviour early before the habit starts to affect incoming adult teeth. Thumb sucking can be limited and eventually stopped by encouragement, rewards, gentle reminders and unpleasant-tasting nail paint available from pharmacies. Sometimes, it just requires some determination and persistence.