An immediate short term impact of child labor had to be a reconfiguration of what it means to be a child. The essence of being able live a childhood free of working conditions that were unregulated and excessive hours as well as beyond difficult daily routines is the most jarring short term impact of child labor during the industrial revolution. Children who should have been learning from members of community or family, or going to school, or even playing games with other kids were working with adults, in hazardous conditions, in filth and unimaginably crowded conditions. This helped to feed the long term impact of understanding how wrong child labor is, and how it must be something avoided. Additionally, the presence of child labor helped individuals understand that there is a unique experience to childhood that should be maintained as far as possible and one element outside of this is making kids compete with adults for jobs that the latter should only be doing.
Of course, they didn't have sociology and stuff like that back then to study this, so we don't know for sure.
I believe that a short term impact of child labor was that the industries that used child labor were able to grow quickly. Part of this was due to the low price of child labor. Another short term impact was, of course, on the children. They were forced to work in hard and dangerous conditions, which must have been quite unpleasant.
In the long term, I think that child labor's impact was not so bad. As the industries became more profitable, people's standards of living grew. The companies innovated and were able to start doing without child labor as they got richer. I think that is one reason why children in the rich world today work less than those at any previous time and place in history.
The short term consequences of child labor were well described in Upton Sinclair's book "The Jungle." Young children were used to climb into machinery into places adults could not fit. As a result they were killed, maimed, lost limbs, suffered dehydration and starvation. They were forced to work long hours and had no childhood. Child hood back then was far from the luxury that it is these days.
Other consequences were that children were sexually molested, an issue not often found in the books. Some children were even impregnated. Parents had little to no control of what happened to their child once he/she left the home. They needed whatever income could help the family to survive.
Long term affects were not so easily determined as like the previous editor stated that there was no one documenting and studying the issue. Once could easily ascertain that many of the grown children turned to alcohol or lived lives of poverty since many were pretty disabled from their jobs.