Try to get a couple parents to help you manage (or siblings if you have any). At scouting we try to have at least 4 adults for 35 kids, which is manageable. Definitely start them with some active games like tag or any variation of it (i.e. cops and robbers). Our kids also love dodgeball and buskruit (wikipedia tells me it's called "kick the can" in english). Having them run around for half an hour or so will get them to release a bit of their boundless energy (and it'll get them thirsty, expect to have to pass around drinks 45-60 minutes in). Try to do as much outside as you can, 35 kids playing inside can get LOUD and quite overwhelming, especially if you're managing them on your own.