24 months Underweight toddler. Age?

Hello docs, My daughter is 2 years old. She just just weighs 8.5kgs. below is her weight history. Birth weight - 2.9kgs Weight at 6months - 6.15kgs Weight at 12 months - 6.9kgs Weight at 18 months 7.78kgs Weight at 23 months - 8.5kgs She is just half of what her ideal weight should be at this age. She looks really small. Height is also 80cms. I give her everything food, fruits, dairy products, nuts everything. even introduced her different textures at different age. Sometimes she eats well but mostly she fusses around. Eats very less quantity. She is very active. Can't sit at a place for more than 2 mins. We had her blood work done at 11 months. Her vitamin D level was low. Given suppliments for this. Since i Breastfeed i took postnatal multivitamins n cal for 3 months pp. Kindly suggest me what can be done to Increase the healthy weight gain. Is this under weight will cause any developmental delays or anything or any other issue in later age ? Please guide me