How much of vitamins c, d, and a can you give a 4 year old and an 8 month old? wanting to build immune system to prevent flu.

See pediatrician: If your kids are well nourished overall, giving them multivitamins will not drastically change their degree of immunity. The flu shot would be more effective than vitamins. If you'd like to give vitamins still, it is not a bad idea for overall health. Follow the package directions for a kids multivitamin and speak to your eight-month-old's pediatrician for a specific recommendation.