Kindergartners themselves might not have been particularly racist (though only might, kids pick up on that shite pretty early, unfortunately), but the teachers or parents that thought it was okay? Probably. Kids I'd maybe give a pass for explicit awareness when they're still like six bloody years old or some crap, but that cuts off somewhere in the teens, if that.
Either way, that's fairly irrelevant to the actions of a 29 year old in the 2000s, which was apparently when trudeau was still pulling that shit. Or most of the people that wore or encouraged fucking blackface since it started snowing up in minstrel shows and junk. You can maybe make the argument of it being racism neutral years ago if you were talking about somewhere not North America or most of Europe or basically anywhere with a substantial english speaking population, or maybe pre-colonization, but on this continent the crap's been racist as hell from day 1 and it ain't slacked off.
Cowboy/indian stuff has its own problems, but we ain't talking that mess. We're talking something pretty specific and it's shit that's been unambiguously racist for its entire history in just about every context. Trudeau is or was racist, flat out. Maybe not the virulent lynching-doesn't-sound-that-bad sort, but the more passive sort that doesn't give a damn to the degree they'd trot out friggin' blackface, yup. It's pretty evident he is or was literally that.
Again, that might not mean other options were worse, but the blowback he's gotten on the subject is deserved. Maybe he's changed in the last twenty or so years, I'unno. Maybe he stumped hard on the problems making a good number of corpses out of canadian minorities and I just missed it. S'possible.