Two of them - Tavares and McDavid - are centermen, and both are NHL All-Stars, so it's easy to see why that happened there. The other two are defensemen, and Ekblad is, indeed, such an exception that he already has NHL hardware (Calder Trophy, 2014-15) on his mantle. Day's development has not been going so smoothly...
I can't speak to his play as a child, because I didn't witness it - although some websites have his statistics from his days at the bantam and midget levels available for all to see - but here's a look at the rough numbers:
The bad: His offensive development took a major step back in 2015-16, prompting him to fall in his draft year, from a projected late first-rounder/early second-rounder to 81st, near the end of the third. Sure, he went back to a half-point/game rate in 2016-17 with a championship team, but keep in mind he's now an adult facing some teenagers and players who are at most two years older than he is, not
By the time he started playing in the OHL, he was already 6'2" and 220 pounds with tremendous speed, which had scouts salivating at the prospect of his further developing; that was forgetting that he still was just a kid, and one who had had fun playing hockey until then. Now came pressure, and accusations of laziness when he failed to meet expectations. Before he was drafted, he took his body fat down from 19% to 12%, which still had him at 228 pounds.
He's now a Memorial Cup champion. Maybe we can take a breath or two and wait until he's 24 or 25 to judge who he becomes as a hockey player and, more importantly, as a human being.
Here he is as a rookie, on card #101 from In The Game's 2013-14 Heroes And Prospects set and CHL Rookie sub-set, wearing the Mississauga Steelheads' white uniform, which he signed in blue sharpie: