The child needs to be evaluated by a speech therapist. Most offer it for free. If Mom fights it just let her know that it will rule out any problems and it's always good to hear how good a child is doing. Sounds like she's in denial and that will only harm her child's progress. If Dad thinks he needs it he doesn't need Mom's premission to get him evaluated. It's best to get therapy for speech as early as possible. The longer they wait the longer therapy will take. The therapists are experts and will be able to spot if this is a speech thing or if there is a physical problem with the shape of the mouth of tongue, which is good to know early as well.
Two of my sons needed real speech therapy.
My second son, now 15, had a lateral lisp. I didn't realize there was such a proiblem because I understood what he was saying because I was with him all the time. I understood his grunts and "words". My neighbors never understood him and I just figured they didn't know him well enough. But when my husband said that he didn't even understand him then I knew he may have a problem. By his 3rd birthday we had him tested and learned that he had a lateral lisp. It wasn't a frontal lisp like Cindy Brady where the tongue presses against/through the front of the teeth. A lateral lisp is where the tongue flattens out and has a lot of saliva and spit like Sylvester the Cat. So he needed specific help to train his tongue to curl to be able to say certain letters and sounds. He had speech from age 3, into early preschool and preschool and through most of elementary school. He progressed quickly but needed to be seen once a week at school to be sure he wasn't going backwards as some kids do.
My 6 year son needed speech therapy from age 2-5. He had a delay and went to a weekly preschool group with other kids like him and picked up quickly! He still has a slight delay but he does not qualify for therapy as it as not 25% or more, so we just work with him at home with reminders.
It's bettter now to get the help as any teasing will be minimal at this age. The kids will be confused before they start teasing at age 5 in kindergarten. But as kids get older they can start teasing so get the help now. It also will interfere with his learning if his speech is not correct, which is the biggest problem and self esteem can go down the toilet.
K. B
mom to 5 including triplets