What can I give my sick kids?

I have two children. They are 4 and almost 2. My oldest just went to the doctor for his check up and was fine. The weather all of a sudden got cold and yesterday it was so freakin hot. I think he has allergies but I am not sure what they are. My husband is allergic to pretty much everything, so is my mom and sister. I have no allergies and i am rarely ever sick. Now instead of just a runny nose, my 4 year old has a hoarse cough and runny nose. Very congested. My 2 year old also have developed a runny nose but has coughed a few times. Other than tylenol and motrin, what can I give my kids to help them? Also, how old does a child need to be before they are tested for allergies?