WASHINGTON — It’s one of the timeless questions parents of babies and toddlers grapple with: How to wean a thumb-sucking child?

Some parents are horrified by thumb-sucking while others think it’s a perfectly acceptable self-soothing method, at least for very young children. But at what point does that endearing and seemingly harmless habit — one your child might have acquired in utero — become a problem? And how do you convince a child that he or she can survive without using that permanently attached pacifier?

Pacifiers of the non-attached variety are a different issue and somewhat easier to eliminate, according to Mary Hayes, a pediatric dentist in Chicago and the national spokeswoman on pediatric dentistry for the American Dental Association.

“I would prefer a pacifier over a thumb because it’s easier to give a pacifier away to a new baby, or the monkey at the zoo, or a fish in the lake,” Hayes said.

Carol Mayer, a speech pathologist in Chicago and author of “My Thumb and I,” says three things determine how difficult it will be for children to give up sucking their thumbs and whether there will be long-term damage to their mouth: how often they suck, how long they’ve been doing it and how intense their sucking is.

We recently spoke with Mayer, Hayes and other experts to find out how, and when, to dislodge that finger. Here are some suggestions:

• Wait until they are old enough. As much as it may bother some adults, thumb-sucking is a perfectly natural and healthy habit for infants and young children, pediatric dentists said.

Hayes said thumb-sucking usually wanes between ages 2 and 4 as children begin talking more and find other self-calming activities. “Sucking is a normal behavior for a young child,” Hayes said. But “some kids carry that need on, and then it turns into a habit.”

Parents should also remember that it’s nearly impossible to reason with a tot about the long-term consequences of something that children find so comforting. “It’s really hard to say to a 3-year-old, ‘If you suck your thumb, you’re going to need braces,’” said Dana Greenwald, a Washington pediatric dentist. “You might as well be speaking Portuguese.”

Experts agree that if a child is still sucking by the time his or her permanent teeth begin to come in, it’s time for parents to take action.

• Be positive and use rewards. Don’t harangue your children or shame them, because that could backfire and send them to closet thumb-sucking or other self-soothing methods such as rocking or nail-biting. Instead, give them control of the behavior and offer praise and rewards for success.

“The child has to want to stop,” Greenwald said. “A lot of them feel helpless, like they can’t stop yet. … Find whatever motivates your child.”

That motivation could be something as simple as putting a sticker on a calendar for every thumb-free day, with the child receiving a special treat after a set number of days. Or use role models as examples, Hayes suggests. “You can point out to them: ‘Does a fireman eat good food? Does a fireman have to exercise? Does a fireman suck his thumb?’” she said. “Promote the idea that people whom they admire don’t suck their thumbs.”

• Do it gradually. If your child is a particularly intense sucker, limit him to sucking only at night, or only in his room.

“Work at a plan where a parent is reminding them, ‘You can do it, but you have to go to your room,’” Greenwald said. “Most kids figure out that they would rather do something else.”

“There’s always an emotional component to this,” Hayes said, “so generally what we suggest is that a parent try to reinforce more age-appropriate calming behaviors, like reading a book or … watching a movie at bedtime. You can say, ‘For this page of this book we’re going to practice not sucking your thumb.’ If you tend to nag the kids about it, they tend to get more anxious and want to do it more.”

• Use a gentle reminder. Using Mavala Stop ($8.70 at Amazon.com), a bitter-tasting clear nail polish, or a strategically placed bandage or special glove that covers only the thumb are other ways to help your child stop sucking. These strategies work best with less intense suckers, experts say.

• Try, try again. Some children can give up the thumb with nothing more than a gentle nudge from a respected adult, and others might require a full-blown intervention.

Don’t frustrate yourself or your child, the experts agree. Just as when toilet-training your child, if you’ve gone a couple of weeks without much success, take a break. Wait a few weeks or even months, then revisit the issue.

“Behavior experts tell us that 21 or 28 days of consistent change will extinguish a habit,” Mayer said. “If you always eat pretzels at 4 o’clock, at the end of 21 or 28 days of not eating pretzels, you’re done with that behavior. It doesn’t mean you won’t want to eat them, but you will have extinguished the addiction.”

Strategies to wean a thumb-sucking child

When to start: Wait until the child is older than 2. “Sucking is a normal behavior for a young child,” said Mary Hayes, a pediatric dentist in Chicago.

First: Use positive re-inforcement like praise, stickers for suck-free days. Promote a role model.

Second: Ease the child away from thumb-sucking to, i.e., sucking only at night or only in his room.

Thirdly: Use reminders like a glove or something bitter-tasting on the thumb.

Finally: Don’t be over-bearing and pushy about thumb-sucking. Take a break and try again later.