It is ok if i give 3 kinds of vitamins to my kids?

NOT OK...: As long as your kids are eating a balanced diet, there is no need of extra vitamin. Sometimes, pediatricians prescribe vitamins for a short period of time while recovering from illness for which kid needed antibiotics. Remember, unnecessary vitamin may harm your child. There is a condition called hypervitaminosis, when too much vitamin is consumed with resultant problems.

Could be toxic: If you give them a good multi vitamin like the chewables once a day that shoulfd be adequate. Too much vitamins can be poisonous to them and make them sick and mess up their young developing bodies.

Hard to say: You don't describe what the vitamins are or why you feel this is needed. Many vitamins that are not needed that day by the body end up in the urine in less than a day. Giving them would likely just be a waste of effort but not toxic. Some vitamins (A,E,D) store up in the body and can produce toxic effects. Please be more specific when you post.