Brother and sister Tyler and Maggie Heath grew up playing music together, and their debut as The Oh Hellos has the loose-limbed, ecstatic energy of two (prodigiously talented) kids goofing around. Yes, the songs here are peppered with dark, occasionally ominous imagery (“The Truth Is a Cave” and “In Memoriam”). But when you hear the rollicking guitars and heavenly “oh-oh-ohs” of “Second Child, Restless Child” or the ebullient choral flourishes of “The Valley,” it’s impossible not to get swept up in the Heaths’ unbridled joy.