My daughter is 4 years old now. Since the age of 1, she has been diagnosed with pneumonia 24 times now between 2 hospitals. I feel for you.
I hope the kids didn't get pneumonia. Sometimes there isn't anything you can do and didn't do anything "wrong". One thing I can think of is to make sure whenever you go somewhere in the public to wash yours and the kids hands before you leave the public building so that any germs that they picked up are washed off before you leave.
Another thing is that whenever you go to the doctor's office, don't let the kids play with the toys. I always took things for the kids to play with and didn't let them touch the things in the doctor's office because I knew sick kids had been playing with them. If they touched the elevator buttons or anything, we stopped and washed our hands on the way out. I didn't get obsessive about it, doing it repeatedly while there, just before we left and it seemed to help. At one point it got hard to keep them from playing with the toys so I told the nurse we were going to go for a walk in the hallway and asked her to call whenever they were ready, that made it easier.
I, also, gave the kids extra vitamin c whenever they had the frst sign of a cold, you can ask your doctor for the kind and amount that is best to use for your children's ages, lots of health food stores and pharmacies sell it in different forms. For a cold, just using salt water mixture drops for the nose and a suction bulb help keep it cleared out. I always ask my doctor or nurse for directions before using home health treatments, they are very supportive of their use.
Hope that helps. God bless you & your family, Lisa