Yeah the low battery warning is extremely obnoxious and not dismissable at all. I don't know who thought this was a good decision!
What's even more crazy is that often when I attempt to silence the low battery warning by placing the Small Child in the charger, it often refuses to begin charging until the battery has been entirely depleted, so along with not being dismissable, even attempting to charge the Small Child does not stop the low battery warning consistently! I believe this is likely a bug, but I haven't yet been able to consistently replicate it to file a bug report despite experimenting with various charging and usage schedules.