More accurately, do you need to take vitamin-mineral supplements? You already get these nutrients from food.
The answer is, it depends. It depends on your diet, exercise, and family history. This decision should be made in consultation with a physician or a trained medical specialist. Likely, you will be told that you get sufficient nutrition from food but should supplement additional vitamin D and calcium. Therefore any extra supplementation, while not likely to be harmful is probably of no benefit.
Online, people often state that they take supplements as a form of health insurance. They note something like "I take vitamins and never get sick." They could also place garlic on their doors to keep thirsty vampires away and claim 100% success.
What about the kids: your own or your charges? That too is a decision that should be customized with the advice of a pediatrician or a physician. Knowledge of the fluoride level in the local water supply and family history and mediacl conditions are vital for the practitioner to select proper supplementation.
Make a thoughtful choice with your medical advisor. Do not be swayed by advertisements or salespersons.
Tomorrow: Discussing herbs, homeopathy, and other self-administered remedies.