2-year old Sophia Polanco prefers her pacifier, while big sister Eileen Polanco likes her thumb. She's 8 years old, and her habit kicks in at night and in school.
"It makes me feel better whenever I'm scared," Eileen said. "When I'm at school and gonna do a little test I get scared cause I may not pass."
"I kind of remind her and she goes with it, then she forgets and then does it when I'm not around," said Eileen's mother Sully.
The older the child, the harder it is to get them to stop, and prolonged thumbsucking can cause misalignment of the teeth and jaw, increasing the need for braces. There's also a health risk.
"When children suck their thumb they create pressure into their mouth and throat and that extends into their middle ear, and it's thought that may increase ear infections," said Dr. Amr Moursi.
But pediatric dentists, like Dr. Moursi, now have plenty of tricks in their dental bag to get kids to stop, starting with behavior modification.
For example, mark the days on a calendar when your child doesn't thumb suck. Then, every few days, give a prize.
If that doesn't work, move on to a special polish that's painted on a child's thumbnail. The bitter taste can be a big turnoff.
There's also a child-proof thumb guard.
"They cant get that nice comfortable feel in their mouth," said Dr. Moursi.
When all else fails, a retainer like device can be cemented on the teeth. It stops a child from placing her thumb in the comfort zone on the roof of the mouth.
As for Eileen, she wants to stop her habit and will try the nail polish deterrent. But for those kids where nothing works: "Sometimes we need to look at underlying causes and some of those children will benefit from a child therapist," said Dr. Moursi.