What Is a Lisp? Understanding Speech Sound Difficulties in Children

When children are learning to talk, it's normal for them to make speech errors. One of the most recognisable speech errors is a lisp. Children with a lisp often have difficulty saying certain consonants, especially the /s/ and /z/ sounds.

Parents often wonder, "Will my child grow out of a lisp?" or "Does my 4-year-old need speech therapy for their lisp?" The answer depends on the type of lisp and your child's age. A frontal (interdental) lisp can be a normal developmental phase for some children, while a lateral lisp is not part of typical development and usually requires speech therapy to resolve.

In this article, we'll focus on the two most common types of lisps in children — interdental and lateral — what causes them, when to seek help, and how speech therapy can support clearer, more confident communication. If you'd like to learn more about general speech sound milestones, see our full guide on speech sound development.

What Is a Lisp?

A lisp is a specific type of speech sound difficulty that affects how the /s/ and /z/ sounds are made. Lisps happen when a child's tongue is positioned incorrectly during speech, that it blocks the airflow needed to make the /s/ and /z/ sounds.

Children with a lisp are usually trying to say the correct /s/ sound, but it may come out:

• Like a /th/ (e.g., "thun" instead of "sun"), or
• With a "wet" or "slushy" quality

The Two Most Common Types of Lisps

Although there are several types of lisps, the two we see most often in children are interdental lisps and lateral lisps.

1) Interdental Lisp (Frontal Lisp)

• The tongue pushes forward or protrudes between the front teeth when making the /s/ or /z/ sound.
• This makes the sound more like /th/ (e.g., "thun" instead of "sun" or "math" instead of "mass").
• Common in preschoolers and can be a normal stage of development up to about 4½ years old.

2) Lateral Lisp

• Air escapes over the sides of the tongue and into the cheeks.
• Can occur on several sounds such as /s/, /z/, /ch/, /zh/, and /dj/.
• Creates a "wet" or "slushy" sound.
• Not typical speech development — a child with this type of lisp should receive an assessment from a speech therapist as soon as possible.

What Causes a Lisp?

Lisps result from the incorrect placement of tongue in the mouth, which can obstruct airflow and distort the pronunciation of some sounds, especially /s/ and /z/.

Other factors that can contribute include:

• Having a close family member with a lisp
• Tongue thrust, where the tongue protrudes between a person's teeth when swallowing or speaking
• Jaw alignment
• Mouth breathing or low tongue tone
• Structural differences such as tongue tie

My Child Has A Lisp. Will They Need Speech Therapy Or Will They Just Grow Out Of It?

It depends on the type of lisp:

• Interdental lisps often resolve naturally as children grow, especially before age 5.
• Lateral lisps are not part of typical development and usually require speech therapy.

If your child is over 5 and still has a lisp — or if you notice a lateral lisp at any age — it's best to seek advice from a speech therapist.

Understanding your child's overall speech development can help you make informed decisions. Our comprehensive guide on Speech Sound Development in Children provides detailed information about typical speech milestones and when to be concerned.

How a Lisp Is Assessed

A speech therapist will carry out a detailed evaluation, which may include:

• Listening to your child's /s/ and /z/ sounds in different words and sentences
• Checking tongue placement and airflow direction
• Looking at oral structures (teeth, tongue, jaw)
• Asking about breathing, eating, and swallowing habits
• Considering your child's overall speech clarity and confidence

If other concerns are present — such as unclear speech on multiple sounds — the speech therapist may look for other speech sound disorders too.

How Speech Therapy Can Help a Lisp

Therapy for a lisp focuses on teaching the correct tongue position and airflow for the affected consonants, then practising until it becomes a new habit.

My Child Has A Lisp, What Can I Do To Help?

• Focus on what your child says, not just how they say it.

• Model the correct sound naturally. If they say "I want to wear the red 'thock'," you can say, "You want the red sock. Let's put on your sock.". Don't worry if they can't say it back or copy you in the right way yet.

I'm An Adult Who Has A Lisp. Is It Too Late For Me To Change It?

Lisps are not only a childhood issue. Some adults still have a lisp if it wasn't addressed earlier. The good news: it's never too late to fix it.

With regular practice and guidance from a speech therapist, many highly motivated teenagers and adults have successfully corrected their lisps.

When to Seek Help

You may want to book an assessment with a speech therapist if:

• Your child has a lateral lisp at any age
• Your child has an interdental lisp after age 5
• The lisp affects your child's speech clarity, confidence, or social participation
• You're unsure whether it's part of typical development

Early support can prevent the lisp from becoming a long-term habit and help your child feel more confident in speaking.

Take our free Communication Milestones Quiz to help you understand your child's overall communication development and identify any areas that might benefit from additional support.

Summary

A lisp may be just one small part of your child's unique voice, but if it's affecting clarity or confidence, speech therapy can help. With the right guidance, children (and adults) can learn to produce clear sounds.