my boy is three yr 3months he understand everything.but he can't talk..he used to say words..but can't speak the full sentences in his own

Question

Accepted Answer

This is normal 
Here are some ways you can encourage your toddler's speech:
Talk directly to your toddler, even if just to narrate what you're doing.Use gestures and point to objects as you say the corresponding words. ...Read to your toddler. ...Sing simple songs that are easy to repeat.Give your full attention when talking to them.

Answer

proper language / speech development will start between 18 months of age to 2 years of age. 
there is no need to worry before that just concentrate on the diet and regular interaction with the child.
also speech and language develops properly with more people available to interact with the child
avoid usage of tv mobile and laptop because they are the most common reasons for delayed speech and language development.

the moxst important thing is that before speech understanding of the commands given by the parents should be present.
by 18 months if the child is not following basic commaxnds then only you have to meet the doctor
requirement of speech therapy will also be discussed by your doctor