Is it a male or female child? If it is male, weight needs to be considered even more as it is going behind 5th centile. If female, its below 25th centile.
I can help you out with the following plan:
3 main meals with 2 snacks in between
Main meals should have, grains(Barley, Buckwheat, Flax, Oats, Pasta, Rice, Sesame), vegetables(Asparagus, Broccoli, Eggplant, Carrots, Peas), meat
proteins (Beef, Eggyolk, Fish, Ham) and oil or butter.
Fat gives more calories in a growing child.
You can give fruits and biscuits as snacks in between.
Cottage cheese and Yogurt can be added up as snacks.
Milk and other dairy products will be helpful once or twice a day.
Your child might need a catch up growth. Increase the portion size and make diversities in cooking meals in different tastes. Better avoid sugar and salty foods.
We need to have a record on your childs growth parameters. You can consult a Nutritionist for further development.