THUMB SUCKING IN CHILDREN 
Is it a problem?
All babies are born with the need to suck. This is called SUCKING REFLEX, which can cause them to put their thumbs or fingers into their mouths.
This is important because babies need the sucking reflex to eat and drink. Thumb sucking also makes babies feel SECURE.
Some babies might eventually develop a habit of thumb sucking when they’re in need of SOOTHING or going to sleep.
Most children grow out of sucking their thumbs or fingers around 2 to 4 years of age.
Beyond that age, this behavior may affect the shape of his mouth or how his teeth are lining up.
Do you know?
Babies even suck their thumb even before birth. 
HOW TO STOP THE HABIT
Prolonged thumb sucking may affect the roof of the mouth (palate) or how the teeth line up. 
The risk of dental problems is related to how OFTEN, how LONG and how INTENSEly your child sucks on his or her thumb.
From the Malaysian Association of Paediatric Dentistry (MAPD) website, it states that if the habit of thumb sucking continues after 2 years, it should be discouraged in order to cease the habit by the age of 3.
Here are some things you can try:
Offer praise and small rewards
Eg: Extra bedtime story or a trip to the playground — when he or she isn’t thumb sucking. Set attainable goals, such as no thumb sucking an hour before bed. Place stickers on a calendar to record the days when your child successfully avoids thumb sucking.
Identify triggers
Some children suck his or her thumb in response to stress. Identify the real issue and provide comfort in other ways — such as with a hug or reassuring words. You might also give your child a pillow or stuffed animal to squeeze.
No teasing or punishment
This may upset your child and is not an effective way to get rid of habits. Putting too much pressure on your child to stop might only delay the process.
Keep hands busy and distract
You can offer a fidget toy to keep his hands busy.
Some children uses sucking to relieve boredom. Distract him with things he finds fun.
See the dentist 
Your pediatric dentist can encourage your child to
stop. For some kids, a chat with the dentist about why it’s important to stop thumb sucking is more effective than a talk with mom or dad.
