The RDA for adults for Vitamin A is 5.000iu (some revised recomendations are even lower). Each Airbornne has 5,000iu so taking it more than once a day could lead to an overdose. The package recommends taking it every 3-4 hours!!! (but not more than 3 doses in a day). An overdose of Vit A can be toxic and even result in death.
Children 4-8 should only have 1333 iu a day so giving them half of an adult Airborne (as the package says you can) will give them almost twice that dose. A dose of Airborne Jr has 1250iu so it should only be given once in a day and should not be given to children under 4. (source) Their packaging does say ages 4-10. I used to give to the boys when they were 2 and 3 though - dont make the same mistake!
You also do NOT want to take your daily multivitamin on a day that you take Airborne as this could definitely cause an overdose. Especially be careful of this with children.
I would not recommend taking Airborne while nursing but that is something you can research yourself if you dont believe me :)
When Im getting sick I take high levels of Vit C. You can also take zinc. I will post more about that soon!