Update: The blogger on my request attached the source of the data (TOI) to his blog post. See here (look at the map). Thanks Arun. Chances are this data comes from ILO (International Labour Organisation).
According to this blog post:
Kerala has the lowest share of child workers with 0.47% of the total population engaged in child labour. North Eastern states have high rates of child labour with Mizoram topping the list with 12.34%, followed by Sikkim (12.04%) and Nagaland (8.48%).
I find it hard to hear that Mizoram tops the list. I asked the blog owner Arun Rajagopal where he got this data. The Mumbai Edition of Times of India, he said.