How do you find out if a school has class 2 seats when the banners only say nursery?

Our two are at different schools right now and the morning runs are getting silly. The plan is to get the younger one into her brother's school for class 2 next June. Every banner and website I've looked at only talks about nursery and LKG. Do schools announce vacancies for the middle classes at all, or do you just call the office and keep calling? I also can't tell whether asking in January is too late or asking now is too early 😅