Holy Guacamole! How did I miss this? Must read the Events section more often at Beaconcitizen. Sewing camp for kids from Needle Arts Guild of Historical Hudson Valley, organized by Mary Ann Kronk (here is her direct blog). It's already started, but she's offering additional end of summer sessions. From the event posting:

"This summer camp is like no other camp being offered this summer!  You will learn to take proper measurements to determine your size/alter a pattern to fit you/read and understand a pattern/lay out a dress, jacket or shirt and put it all together. "

And, they are taking breaks for swimming. Perfect!