Nearly everyone in the sprawling ensemble comedy “Mother’s Day” (Open Road) harbors a secret.

They are, quite often, terribly complicated mysteries involving racist beliefs, homophobia and even children abandoned at birth. Each story line could, in theory, be a compelling and instructive drama on its own terms.

Garry Marshall’s uneven direction, however, added to a discursive script by Tom Hines, Lily Hollander, Anya Kochoff and Matthew Walker, turns all of this into a leaky slop bucket of bromides.

Not only are none of the themes seriously examined, some of the characters are given equally short shrift. This is particularly noticeable with regard to the few African-Americans on screen. They’re always on the sidelines of the plot, and appear to be written only as wisecracking comic relief.

In the manner of Marshall’s “Valentine’s Day” in 2010 and “New Year’s Eve” from the following year, there are six subplots, with more threads than a Tolstoy novel. This time, the setting is the upscale Buckhead neighborhood of Atlanta.

Sandy (Jennifer Aniston) and Henry (Timothy Olyphant) are divorced and share custody of their two sons on the friendliest of terms. But conflict develops when Henry announces he’s married the much-younger Tina (Shay Mitchell).

Jesse (Kate Hudson) and Gabi (Sarah Chalke) are sisters who live next door to each other. Both are keeping secrets from their clueless parents, bigoted Texans Flo (Margo Martindale) and Earl (Robert Pine).

Jesse is married to South Asian doctor Russell (Aasif Mandvi) with whom she has a son and shares a stepson; Gabi is in a long-term lesbian relationship with Max (Cameron Esposito). But Jesse has told her parents she’s engaged to a lawyer, while Gabi’s cover story involves a fiance named Stan.

Fledgling stand-up comic Zack (Jack Whitehall) has an infant daughter with — and longs for a marital commitment from — live-in girlfriend Kristin (Britt Robertson). Kristin has abandonment issues because she’s not sure who she really is. She was adopted, and she knows the identity of her biological mother, but is afraid to meet her.

While the screenplay presents an ultimately positive view of marriage, other arrangements clearly at odds with scriptural values, though they may be dealt with only fleetingly, are given an unthinking pass.

There’s no question of an agenda; cohabitation and same-sex unions, treated as marriages, are simply presented as aspects of contemporary society that the audience is meant to take for granted. Well-grounded grownups will know how to assess — and resist — this skewed thinking.

The film contains tacit acceptance of immoral lifestyles, some distasteful humor, at least one rough term and occasional crude language. (L, PG-13)