Yet thumb-sucking is normal for kids, regardless of political affiliation. Most generally stop between ages 2 and 4, according to the American Dental Association. So even little Jack Edwards has time on his side.

Parents tend to panic, though, when their child is old enough to go to school and is still sucking. We know of one woman who had her orthopedist father put a cast on her daughter's arm. It didn't work, and her daughter sucked her thumb until she was 8.

"We find that with most children, by the time they're 4 to 6 and they get to be school-age, the habit will tend to slow and they stop themselves," says pediatric dentist Michael Berry in Parkville, Mo. "We find that peer pressure kicks in ... they don't want to seem like a baby."

That's what happened to Juli Sackman's son about 20 years ago. His thumb-sucking never bothered her, and nothing, she says, made her angrier than to have other adults try to correct him, even to the point of grabbing his wrist and pulling the thumb out of his mouth while she held him in her arms.

Sackman, a harp player who lives in Lee's Summit, Mo., figured the thumb was her son's way to soothe himself—a sign of his self-sufficiency, she thought—so she let it be. And when he went off to kindergarten, he decided on his own that his thumb habit was not "socially acceptable," and he stopped.

Dentists tell parents that thumb-sucking needn't be a concern unless the child's permanent teeth have come in. Then the habit can cause dental problems like cross bites or buck teeth. "A thumb habit will move teeth, just like braces do," Berry says.

So how to get them to stop? Sorry, there's no sure way.

You can try coating the thumb with one of those bitter medications, but Berry doesn't know one parent who has ever succeeded with them. You can try covering the thumb with a "sleep-time" puppet to keep it out of their mouth overnight, but kids tend to pull it off.

Whatever method you try, don't make a big deal out of it, dentists say. Ridiculing or punishing a child will only make him more anxious. And what's he going to do to comfort himself? Suck his thumb. Praising a child when he doesn't put his finger in his mouth is more effective than scolding him when he does.

"One of the most effective ways is basically bribing the child," says Berry, a fan of behavior modification, "because you've got to get the child on your side to stop the habit."

Identify the time of day they suck their thumb the most, point that out to them and say "we're going to try to not suck our thumb for this time period," he says.

Offer small rewards for each step they take successfully. (No candy, please.) Once they succeed, walk away from the situation for a while, then come back to it. Next time, set a new goal to have them stop sucking for a longer time; offer a larger prize. And so on.

"It could take months," he says. "We find the longer it takes, the easier it is going to be for the child. You don't want to be too intensive. You want to take your time with it."

Bridenstine in Lenexa tells his parents to get a calendar, a set of stickers "and say, 'Little Susie, it's time to stop sucking your thumb. Every time you stop sucking, you get a sticker. If you get seven stickers in a row, you get a reward.' The goal is to have the entire calendar plastered," he says. "For a lot of kids, that's a game to them. Without their even knowing it, you have to make it a game, make it fun."

The first month will be disastrous, he tells parents, but stick with little Susie.

As a last resort, dentists can prescribe mouth appliances designed to discourage the most devoted thumb-sucker. Typically cemented behind the upper front teeth, some act as simple barriers, while others have pointed "rakes" just sharp enough to discourage a trespassing thumb.

And sometimes, a simple talk from Dr. Dentist is the fix.