ABC’s new family sitcom, “United We Fall,” starts from a fairly thin premise: It follows a married couple, their two young children, and one in-law per spouse, as they cope with one another. This is fairly thin stuff, but it’s buoyed by the charms of the cast. “United We Fall” lacks, perhaps, enough of a hook to instantly compel viewers, but its low-key pleasantness makes it better than replacement-level. 

Will Sasso and Christina Vidal Mitchell play Bill and Jo, parents of two daughters (played by Ella Grace Helton and the pair of child actors Ireland and Sedona Carvajal). Their generally low-key approach to parenting is perpetually stepped on by Bill’s mother Sandy (Jane Curtin) and Jo’s brother Chuy (Guillermo Diaz), both of whom push the family — Chuy towards an optimized, test-prepped version of modern excellence, Sandy towards a sort of benevolent mania. Sasso and Vidal Mitchell share an amiable chemistry as not just lovers but teammates in parenthood’s exhausting relay race. And though she’s only in fleeting scenes in the first two episodes, Curtin, of “Kate & Allie,” “Third Rock from the Sun,” and the original cast of “Saturday Night Live,” is among the most compelling reasons to watch, bringing a taut certainty to each of her increasingly offbeat pronouncements (and occasionally being proven right). A future version of this show, should it be given time and space to evolve, will hopefully include more of her, and broaden out her character; she’s already got the wisecracks down. 

There’s a certain slackness at the heart of “United We Fall” — for all the eventfulness of these parents’ lives, Sasso’s and Vidal Mitchell tend to play parenthood as an exhausting process to be borne with a weary smile. The show’s executive producer, Julius Sharpe, is a veteran of various Seth MacFarlane projects (“Family Guy” and “The Cleveland Show” among them), and brings with him those shows’ looseness of plot, if not their cynicism. (There’s also a touch of their vulgarity, shot through with an ABC-family-lineup dose of sweetness; the first episode sees one of the children getting a somewhat commonplace injury of the lower intestine, caused by constipation.) The meanderingness works towards the show’s view of family life as perpetually catch-as-catch-can; in all, “United We Fall” may not in its first two installments represent a startlingly new way forward for the sitcom, but it fulfills the brief pleasantly enough.