There are many interventions that can help a child who has developmental delay. The most important thing is the earlier the better. As soon as you discover that your child has a delay in any area of development, whether it be in their growth motor skill area, their ability to walk and run and climb or in their fine motor skill area, their ability to possibly feed themselves and do puzzles or hold a pencil. Or in their social skill area which is their ability to play with others, whatever area their delay is, it's really important is to first have them be evaluated by a developmental pediatrician or a licensed psychologist who can do a psycho evaluation on your child.
After that is completed, those licensed professionals either a developmental pediatrician or a psychologist can assess what delays your child may have and refer you to the appropriate therapist who then can evaluate that domain of development and then treat those specific delays.
Again, the most important thing to note is that the earlier the better and begin the process by speaking with your child's pediatrician.