Can we give threptin biscuit to a 13 month old kid? Since it's high in sugar and protein, would it be too heavy for the child to digest?

Yes charu. But limit the consumption

You can but not more than two to three per day. The protein content will be heavy to process at one go if more than that are given. You can try other options like khakra or puffed rice or even roasted lotus seeds made into small pieces.