Tongue to palate may not yet be instinctive.

Because the younger has to touch the roof of the mouth the hard palate. Some kids has tongue problems and have difficulty touching their palate and need exercise.

Not to worry why, but a speech pathologist is needed to correct this articulation error. You should reach out to one who specializes in early childhood development. Get recommendations from a university who has a master's degree program in speech pathologist, the board of education in your community, or from your pediatrician.

/L/ is a later developing sound (comes around age 5) but you could model for him placement of tongue (right behind front teeth on alveolar ridge) for the production of /l/ in words and segmenting the sounds "l" ike

Hi,

The /l/ sound is a difficult sound for most 4-year-old children to pronounce. It develops between the ages of 3-6. If you are concerned with his ability to make the /l/ sound, I would recommend contacting a speech-language pathologist to determine if he is eligible for speech therapy based on a speech and language evaluation.

The "l" sound developmentally doesn't occur for boys until around age 6. It is a 'glided' consonant which is harder to produce.

It it hard to say the reason without having completed a comprehensive speech and language evaluation. Please request to your pediatrician a prescription for a speech evaluation and if the severity of the condition is not developmental then he might need treatment sessions. The /l/ sound in my opinion is one of the easiest to target and all he needs is skilled therapy.