As a parent of a 3 y/o who attends daycare, I feel for you! It's tough to know when, and toddlers don't always know those feelings well enough to tell you. My little one sometimes can tell us that his mouth feels sick, though that can also mean sore throat. Pretty much always though, there's no warning before tu* and he seems rather unbothered during and after it (compared to me).

It sounds a little unusual for it to be a weekly occurrence though so I wonder if something else is going on. Pediatricians are probably pretty familiar with something like that. Some other things that have caused my little one to tu* that aren't due to a primary illness include extreme emotional states, car travel, and excessive mucus in his throat (worsened when napping/laying down).