The “th” sound is one of the last sounds children master in English, typically not fully developing until around age 5 to 7. If your child is substituting “f” for “th” (saying “fumb” instead of “thumb”) or “d” for “th” (saying “dat” instead of “that”), that’s completely normal for preschoolers and even early elementary-age kids.
Why “Th” Develops So Late
English has a rough developmental order for speech sounds. Early sounds like “m,” “b,” “p,” and “d” show up around ages 1 to 3 because they only require simple lip or tongue movements. Sounds like “s,” “r,” “l,” and “th” come much later because they demand more precise control of the tongue, airflow, and voicing all at the same time.
The “th” sound requires a child to stick just the tip of the tongue between the front teeth, keep it relaxed, and push a gentle stream of air over it. That’s a surprisingly tricky motor skill. Young children’s tongues and jaws are still developing the fine coordination needed to hold that position while also controlling their breath. It’s the same reason “r” and “l” also tend to be late arrivals.
Two Types of “Th”
There are actually two distinct “th” sounds in English, and most children don’t master either one until at least age 5.
- Voiceless “th” (as in “thumb,” “think,” “bath”): The tongue sits between the teeth and air flows over it without any vibration from the vocal cords.
- Voiced “th” (as in “this,” “that,” “mother”): The tongue position is identical, but the vocal cords vibrate at the same time.
The tongue placement is the same for both. The only difference is whether your child engages their voice. Children often acquire one version before the other, and the voiced “th” in common words like “the” and “that” sometimes emerges a bit earlier simply because those words appear so frequently in everyday speech.
Common Substitutions Kids Make
Before children can produce “th” correctly, they replace it with easier sounds. Speech-language professionals call this “stopping,” where a child swaps a sound that requires continuous airflow for a simpler, quicker sound. A child might say “dat” for “that” or “tum” for “thumb.” Others substitute “f” or “v,” producing “fink” for “think” or “bruvver” for “brother.”
According to data from the American Speech-Language-Hearing Association, children typically stop making these substitutions for the voiced “th” sound by around age 5. The pattern of replacing fricative sounds (the category “th” belongs to) with stop sounds is considered a normal part of phonological development up to that point. If your child is 4 and saying “dis” instead of “this,” there is no cause for concern.
What the Typical Timeline Looks Like
Most children follow a general pattern with “th” sounds:
- Ages 2 to 4: Substitutions are completely expected. Children are working on earlier sounds and haven’t attempted “th” in a consistent way.
- Ages 4 to 5: Some children begin producing “th” correctly in certain words, especially familiar ones. Errors are still normal.
- Ages 5 to 7: Most children can produce both “th” sounds correctly and consistently in conversation. The National Institute on Deafness and Other Communication Disorders lists “th” among the sounds children are still working on even as they enter school, alongside “r,” “l,” and “s.”
The benchmark most speech-language professionals use is the age at which 90% of children produce a sound correctly. For “th,” that threshold falls later than nearly every other English sound.
When Substitutions Might Signal a Problem
Because “th” is such a late-developing sound, most speech-language professionals won’t flag it as a concern in a child younger than 5 or 6. A 4-year-old who says every other sound correctly but still swaps “f” for “th” is right on track.
There are situations where the picture looks different, though. If your child is older than 7 and still consistently unable to produce “th,” or if the “th” difficulty is part of a broader pattern where multiple sounds are unclear or missing, that may point to an articulation or phonological issue worth evaluating. Similarly, if your child seems frustrated by their own speech or if other people have significant difficulty understanding them at age 4 or older, getting a screening can provide clarity.
How “Th” Is Taught When Practice Helps
The physical technique is straightforward. The child places just the tip of the tongue lightly between the upper and lower front teeth and blows air gently over it. The tongue should barely peek out, not stick way out. For the voiced version, the child hums or adds voice while maintaining that same position.
Many children pick this up naturally through everyday exposure and practice. For those who need a bit more structured help, speech-language professionals often start with the sound in isolation, then move to the beginning of words (“think”), the end of words (“bath”), and finally into full sentences and conversation. Mirror practice helps because children can visually check whether their tongue is in the right spot. The whole process feels less like therapy and more like a series of short games, especially for younger kids.
One thing that can slow progress is if a child presses the tongue too hard against the teeth, which blocks airflow and produces a “t” or “d” instead. The key sensation is a soft, breezy feeling between the tongue and teeth, not a firm press.