S.H.
There is viral Pneumonia and Bacterial Pneumonia.
Yes, it can be very contagious.
The organism that causes Pneumonia, can be very contagious.
And it can be very dangerous.... ie: ending up in the hospital.
Children, often display symptoms different than adults. So there is no cut and dry 'symptoms' but a Doctor needs to listen to their chest and symptoms as a whole and or x-ray etc.
Some people with Pneumonia, "seem" normal...but they are very sick. This is called "walking Pneumonia" and it is also very dangerous.
I have had Pneumonia and so has my Mom. My Mom was 'fine' but had a fever and slight cough... it would not go away. She finally went to the Doctor... and almost ended up in the hospital.
For me, I almost did. I had to take antibiotics.
Here is a link about it per children:
http://www.askdrsears.com/html/8/T083800.asp
all the best,
Susan