If you r giving proper nutrition then it may be a physiological condition..your children will catch up growth in a few years...
Otherwise it can be due to pinworm infection..
You can do a course of tablet albendazole ..after consulting a doctor..
Along with that I would like to know what is their daily calorie intake..and what type of food you provide them
Disclaimer - The content is not intended to be as a substitute for a
professional medical advice, diagnosis, or treatment. Always seek
the advice of your physician or other qualified health provider
with any question you may have regarding your medical condition.
Never disregard professional medical advice or delay in seeking
it because of something you have read on the website.