Greetings
The provided image displays a query from a mother who did not give her baby
vitamin D for the first 4 months and is asking if this caused harm, how to safely start now, and what precautions to take.
Missing vitamin D for the first few months is a common occurrence and generally does not cause immediate, lasting harm if addressed promptly.
It is completely fine to start giving the drops now, but you must strictly avoid trying to "catch up" on missed months by giving double or larger doses, as high doses can be toxic.
The standard recommended daily dose for infants is 400 IU (International Units) per day, but you should always verify the concentration on the physical label since some brands require a full dropper while others require only a single drop.