This paper presents a nonlinear control scheme for multiple mobile manipulator robots (MMR) moving a rigid object in coordination. The dynamic parameters of the handled object and the mobile manipulators are estimated online using the virtual decomposition approach. The control law is designed based on an appropriate choice of the Lyapunov function candidate. The proposed control design ensures that the position error in the workspace converges to zero, and the external force error is bounded. Numerical simulations and an experimental validation are carried out for two mobile manipulators transporting an object in order to show the effectiveness of the proposed controller.