It was “Kid’s Opening Day” at Camden Yards on Sunday afternoon, which should have been a perfect time for the rebuilding Orioles to show that their kids are all right.

Instead, they wilted under another shower of home runs as the Yankees completed a sweep of the three-game series with a crazy, lopsided 15-3 victory that pushed the Orioles under .500 for the first time since the season opener at Yankee Stadium.

Right-hander Domingo German flirted with a no-hitter until the sixth inning and catcher Gary Sánchez had three of his team’s seven homers as the Yankees atoned for losing their home-opening series to the Orioles (4-5).

The Yankees (5-4) had 14 home runs in the series, which devolved into a full bullpen meltdown in the final innings Sunday. Manager Brandon Hyde was forced to use utilityman Hanser Alberto to pitch in a ninth inning that featured two homers and brought Sánchez to the plate with a chance to hit a record-tying fourth home run.

He got a fat pitch, but popped it up to medium left field.

Hyde said afterward that he didn’t have much choice but to save the rest of the bullpen for the next series against the Oakland Athletics, but he wasn’t happy about it.

“Yeah, that stinks,” he said. “Alberto picked us up big time, though. Unfortunately, those things happen throughout the season, but obviously, you hope it’s a really rare occurrence and happened to us today.”

Orioles starter David Hess, who did not give up a hit over 61/3 innings in his first start, got through the first inning, but he could not keep the ball in the park in the second.

He allowed a leadoff homer to hot-hitting shortstop Gleyber Torres and a one-out solo shot to outfielder Clint Frazier, who delivered the knockout punch Saturday night with a three-run homer off Miguel Castro after the Orioles had staged a late-inning comeback.

Frazier also had a huge day, homering again in the ninth for his third home run in a span of six at-bats dating to that game-breaking home run.

The Yankees weren’t through with Hess. Brett Gardner opened the third inning with a double and Sánchez hammered his first of his three bombs — a two-out, two-run shot into the left field seats.

Those were the 17th and 18th runs scored by the Yankees in the series and every one of them crossed the plate on a home run. The Yankees finally proved they could get an RBI single when Frazier drove home Torres with the fifth Yankees run of the game in the sixth inning.

Hyde didn’t make any excuses for the performance of his young pitching staff.

“The bottom line is you’ve got to execute,” he said. “I feel like we were ahead in the count a lot of the series. We went two strikes, guys battling, but you just can’t miss in the middle or the other side of the plate to good players. They’re going to hurt you. We did that way too often during this series.”

Hess lasted five innings and allowed four runs on five hits. He struck out two and walked one on the way to evening his record at 1-1.

“I just left a couple fastballs up and a hanging slider,’’ Hess said. “That’s a team right now that’s hitting well right now and they didn’t miss.”

Though he allowed a small fraction of the final run total, Hess said the home run barrage started while he was on the mound and took responsibility for it.

“I think for me personally, I think I need to set the tone a little bit better. Going out there and giving three home runs in the first few innings like that, it’s tough to come back from that as a team. So, I think a lot of that is on my shoulders.”

German did not allow a base runner until there was one out in the fifth and did not allow a hit until Alberto — who started the game at second base — lined a single to center with one out in the bottom of the sixth.

By that time, the Orioles were into their bullpen and it wasn’t going any better. Mike Wright came on to start the sixth and allowed the run-scoring single to Frazier. He would also serve up the second Sánchez home run in the seventh before giving way to newly acquired right-hander Dan Straily, who also struggled and allowed three straight two-out hits before recording the final out of the inning.

Straily also served up a homer in the eighth inning to Sánchez, who already had his 11th multi-homer game but had never before had a home run hat trick.

When the O’s finally rallied for three runs in the bottom of the seventh, it still wasn’t pretty. The first run crossed the plate on a passed ball and the second run scored on a wild pitch. The only run-scoring hit was delivered by Alberto, who has hit safely in all five of the games this season in which he has had a plate appearance. He has seven hits in 14 at-bats.

The Orioles fell to 4-5 with their fourth straight defeat, but this was the first time they looked completely overmatched. Hyde has expressed pride in his players for the way they’ve competed through the first three series of the season, but now they’ll have to show some resilience when they open a four-game home series against the A’s on Monday night.

Though Hyde said that Alberto saved the bullpen to pitch another day, he did not rule out a roster move to add another fresh arm.

peter.schmuck@baltsun.com

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Read more from columnist Peter Schmuck on his blog, “The Schmuck Stops Here,” at baltimoresun.com/schmuckblog.