Actually we wouldn't for several reasons. Market pressure from consumers boycotting such companies, not to mention the companies themselves desire to produce the best product and gain the most market share. Capitalism would control the wage market just as any other market. Children could not, and would not in some instances, be able to compete with skilled workers
Uh...children weren't hired for skilled labor. It's not like they were hiring 7 year old craftsmen. There is and always will be a market for jobs that can be done by anyone.