Brooke Mueller has just declared nuclear war in her child custody dispute with Charlie Sheen -- she's accused Denise Richards of abusing her twins and the 2 other daughters Denise had with Charlie ... sources tell TMZ. Law enforcement sources say cops came to Denise's door Tuesday night and told her they were there to question her about a child abuse claim, lodged by Brooke. Denise did not let them inside because her daughters were there. We're told Denise walked outside and told cops the claim was "ridiculous" and "vindictive" -- that the L.A. County Dept. of Children and Family Services was already handling the dispute ... a dispute that started after Brooke was stripped of custody after a raging drug problem flared up yet again.