Some kids are slow to learn to speak. This could be just natural progression and could fix itself with growth, but it is important to make sure there is no medical cause, such as hearing loss. Most speech therapists will suggest you get an audiogram done for your child to make sure. This is particularly important if kids in your extended family have had grommets for glue ear (fluid behind the ear drum).
Another important cause of slow speech development is sleep apneoa. If you child’s sleep is restless and interrupted, it is hard for them to concentrate in the day time. One of the most important learning tasks for little kids is speech development. They have a hard time keeping up with their peers because they are so unrefreshed by sleep. Adults with sleep apnoea get very tired in the day time, whereas kids get hyped up and cranky. No wonder it is difficult for them to concentrate and learn.