Kyle Richards -- Moms Can Still Dress Trashy on Halloween

"Real Housewives of Beverly Hills" star Kyle Richards won't let 4 children stop her from slutting it up on Halloween -- in fact, the 44-year-old tells TMZ, she's already purchased her risque costume for 2013.

Richards was at an event in L.A. Wednesday night when we asked how sexy a mom should dress on All Hallows' Eve -- and Richards said she had ALREADY purchased her costume from Trashy Lingerie in L.A., a store famous for its slutty duds.

But she says she did restrain herself a LITTLE for the sake of her kids, adding, "I ended up with [a more conservative costume] because I am a mom."

Of course, "conservative" at Trashy Lingerie just means your ass isn't showing ... completely.