The Kopecky Family Band. Photo by Will Morgan Holland.

The second track on the debut album by the Kopecky Family Band is the mid-tempo number "Heartbeat," pleasant but unremarkable until the two-tiered bridge, which ultimately explodes with what sounds like a theremin.

It's actually co-founder Gabe Simon whistling, multitracked and treated with reverb, and those 15 seconds demonstrate a maximalist tendency - understandable for a six-person band with members who play several instruments. The album starts with horns and cello, for instance, before the guitar rock kicks in, and the record employs an expansive sonic palette.

But the key thing about that whistling is that it's right, the perfect touch at the perfect moment. Beyond the typical mix of loud and quiet songs, the Kopecky Family Band on the vibrantly dynamic Kids Raising Kids (out April 2 on ATO Records) has a judiciously sharp sense of how much or little songs require; adventurousness is tempered by discipline.

"Change" is acoustic guitar, some ethereal atmospherics, and vocals - anchored by the inherently poignant singing of Kelsey Kopecky. Straightforward opener "Wandering Eyes" has a swagger bordering on stalker menace. "Are You Listening?" finds Simon whistling again, but in a conventionally tuneful way.

"That's the dynamic of the record: to get that simple or to get as a big as a song like 'Hope' - multiple layers, tons of strings, tons of keyboards ... ," Simon said. "There have to be those moments when you say, 'Does it need everything? ... Can this song survive just by itself? Or does the song need these layers to build it into something great, ... memorable?' That's what I think is cool about the record: It has both of those things. That's what six people allows to happen."