Because this question was posed I, being an obsessive researcher, started reading about copyrights. I found that even if you don't sell the item it's still infringement. Making a profit is only a factor in determining monetary damages. Yes, the shirts are copyright infringement with no gray area on that issue. However, if the Disney clip art pack offers T-shirts as a project, that might be the green light. Disney is one of the companies with many restrictive copyright rules, so you have to read their fine print. We have a Disney Dalmatian Print Shop, but T shirts aren't a project offered, so if I use it to make one, I'm infringing.
Does all this mean I'm not going to make my kid a special birthday shirt with Disney characters? I'm not sure. I'm more likely to make their scrapbooks than the shirts.