Hello
Thanks for writing to H.C.M.
I read your query regarding 
sore throat, dark colored phlegm, chest congestion and 
cough.
As per your symptoms it appears as you are suffering from 
respiratory tract infection. this infection has involved both upper and lower respiratory tract. Initialy you were having dark colored phlegm which later became pinkish this indicates blood in phlegm. Your 17 months old kid is also having phlegm this favors air born cross infection.
You are advice to do these investigations-
(a) X-Ray Chest ( P.A.View ).
(b) Culture and sensitivity of phlegm.
(c) Blood -CBC, 
ESR Blood sugar ( F & PP ).
Besde this a thorough examination is necessary to get positive clinical findings and than there co-relation with above investigation will tell us about dignosis and accordingly treatment may be plan.
Your kid is also having cough with phlegm so that should also be clinicaly examined to shave the child from complications of respiratory infections.
I hope this answers your query.
Regards.