Wash hands. The most important thing to remember when preventing sickness is to wash your hands frequently and remind your children to wash theirs, especially before eating. Teach your child to sing "Row, row, row your boat" once through while washing, to prevent the quick rinse that children are known for. Use a baby wipe on a young child's hands or, occasionally, an antibacterial hand wash (limit use, however, to the times when you really need it. Overuse of these hand washes, like the overuse of antibiotics in general, means killing off the "easy" bacteria, and leaving the more hardy ones, resulting in "super bacteria" that don't die when exposed to antibiotics).
Wash toys. If your child is still young enough to put toys in her mouth, ask about the other child's health status before going for a play date, and, if your child is in daycare, check on the toy-washing policy. Some schools have a seasonal "toy wash" when each family takes home a bag of toys for a spin in the dishwasher or washing machine.
Catch fluids. Teach your children to cover their mouths and noses when sneezing or coughing. "Catch that sneeze, catch that cough!" I tell little ones, as I demonstrate sneezing into my elbow. With practice (which they'll probably get plenty of this season), even many two-year-olds understand this technique.
Eat right. Of course, remember how important nutrition is during cold season. There are hundreds of viruses going around each winter, and good nutrition is vital to giving your and your child's immune systems a fighting chance against them.
Make sure to include plenty of fresh fruits and vegetables in your diet. Clementine oranges available in the fall and winter are good for vitamin C and easy for kids to peel on their own. Whole grains, like brown rice and whole wheat breads, are good for our bodies as well as being satisfying "heavier" foods that give lasting energy on colder days. If you're pregnant, don't forget to take your prenatal supplement, and if your child takes vitamins, be mindful not to forget her daily doses; that extra boost can be helpful now!