I've been quilting since the early 90s and I can just tell you that the LQS fabric will last longer and hold the color longer than anything you buy at Joann's or Hancock's. Long ago, I had a fabric that was the same print at an LQS as at Hancock's. The color faded much faster. You could feel the difference after washing. However, if budget is your most important issue, don't beat yourself up for using fabric at Hancock's or Joanns (just avoid the calico wall, if you can). Both have some better quality fabrics. Save the quilt shop fabric for something more for an heirloom or for yourself. For a kid's quilt though, not a problem. They will be on to some other theme by the time the quilt wears out.
I do occasionally get fabric at Joanne's and Hancocks. Sometimes it's a print I need for a themed quilt. However, I can pick up plenty of fabric on sale at the quilt stores - I want them around because they provide services and selection for me that the chain stores can't.