Then, I would suggest u to take yr child to see 中醫. My cousin suffered from this when he was as little as yr child. My grandma-in-law and his parents tried so many ways but still could not improve.
One day, we had gathering and I asked them to try my 中醫. It worked. My cousin was 100% recovered then. The 中醫 asked him to take "野山花旗蔘燉吉??鮑" Frankly, it was quite expensive but it did help him. My uncle told me that my cousin took around 10-15 dosages and costed totally around $6000. But now he is around 7 yrs old and has no probem since then.