Don't think you're going to find a decent non-magnetic case.
I'd buy a watch and put your phone on vibrate. One vibe for emails, texts, etc, and two vibes for phone calls. You won't know if it's specifically the daycare but at least you'll know you received a phone call. If you need to glance at your phone all the time to check the time, I assume you can glance at it to see who the call is. After the 2nd vibe, look to see who's calling.