As gross as this may sound, you can often tell if your toddler's sniffles are something more serious by the color of the mucus. If it's clear, have no fear; that usually signifies allergies. And if it’s cloudy, it’s probably a cold.
If the mucus is yellow or green or worse, however, your child may have a sinus infection — and that's when you should get your pediatrician involved. The doctor will want to do a physical evaluation, and possibly take an X-ray, to see if it's necessary to prescribe some antibiotics. You should also always call the doctor if your child has a temperature of 101 degrees or higher, which is rarely the result of allergies or a cold.