I present splitting theorems for mean convex subsets in RCD spaces. This extends results for Riemannian manifolds with boundary by Kasue, Croke and Kleiner to a non-smooth setting. A corollary is a Frankel-type theorem. I also show that the notion of mean curvature bounded from below for the boundary of an open subset is stable w.r.t. to uniform convergence of the corresponding boundary distance function.