NO NOT NECESSARY ATALL. as u said ur child is healthy fine and playful and not becoming sick frequently, i think he needs nothing except good home made food( a complete diet), medicines(may it be vitamins
) r given to the needy(deficient persons) , and ur child is not among those. all those GREAT PEOPLE , politicians, scientists, adventurous persons, doctors , engineers , ur great fore-fathers might not have taken multivitamins, to be at the place where they were. ur thoughts might be advertise driven, or mothers of more healthier children( more weigh dosnt mean more healthy- both positive and negative sides exceeding normalcy is abnormal at any age). yes good tonics are buttermilk, honey, milk, soups, fruit juices, raw vegetables,fruits,dry fruits(any eatables that r natural. ultimately natural vitamins are more bio-available and do not harm.