hello dr,my son is 3 years 7 month old now..he started to speak the words on his 2 years 6 month old..he started to speak communicative words on his 3 years 3 month old..now he is speaking all the words,telling all his frnds name,telling the names when am showing pics r objects..even he is saying parachute wen its passing by..he is speaking two words jointly now only..at what age can i expect the sentence he will speak?