A child's size 12 is 7.33 inches in foot length. The issue for the leg and width, though, is gauge. If you're getting 8 sts = 1", then I would find a child's pattern that was also that gauge. Try www.knittingpatterncentral.com
for free patterns.
Oh, and it's "provisional" cast on. It means temporary or not fully worked out. Provincial means local, unsophisticated, rustic. Well, come to think of it, that could apply to that cast on, too!