Thank you for coming out and auditioning. I've had the pleasure of working with you all recently, and (especially without plays fully picked yet), I don't know how much benefit it will be to have callbacks at this time. In fact, it might be nicer to just have an afternoon free (or filled with homework and naps). So do that. Take a free Thursday afternoon.
Regardless, you are all being considered for roles based on your auditions. Thank you for sharing your talents, and I look forward to working with you all again very soon.