Can I give this to my baby alongside a multi vitamin that already contains vitamin d?
Please check the combined level of Vitamin D isn't too high. If you give your Baby 2.5ml (half tea spoon) of Opti3 Liquid, that will provide 2.5mcg (100iu) Vitamin D3. As long as the combined level that includes the multivitamin is around 5-7.5mcg, that will be fine. It is best to consult your Doctor though when combining supplements.