My 2 year old needs extra iron (tested anemic) and we do these iron drops:
https://www.amazon.com/gp/product/B00BTMKDUU/ref=oh_aui_search_asin_title?ie=UTF8&th=1
He loves them and we have no problem having him take them. They do stain, so I tend to give it to him while he's in the bath each night, and then brush teeth relatively soon afterwards.
Obviously it's not a multi-vitamin, but it'd solve the iron issue.