Some children find thumb-sucking comforting, and of course there can be times when they need to self-comfort. However, thumb sucking can also put pressure on their front teeth and start pushing them forward. Which could mean they’ll need to wear a brace for a period of time, to move them back.
If possible, it’s best to avoid thumb-sucking, and try to encourage them to break the habit if it’s already started. Try talking to your child about it. Help them understand why they need to stop, and gently point out when you see them do it so they gradually learn to stop. If you’re having trouble, try giving a reward for each day or week they don’t suck their thumb. Helping them feel like they’re doing a good job.