This paper proposes a general modeling approach for locomotion dynamics of mobile multibody systems containing passive internal degrees of freedom concentrated into (ideal or not) joints and/or distributed along deformable bodies of the system. The approach embraces the case of nonholonomic mobile multibody systems with passive wheels, the pendular climbers, and the locomotion systems bioinspired by animals that exploit the advantages of soft appendages such as fish swimming with their caudal fin or moths that use the softness of their flapping wings to improve flight performance. The paper proposes a general structured modeling approach of MMS with tree-like structures along with efficient computational algorithms of the resulting equations. The approach is illustrated through nontrivial examples such as the 3-D bicycle and a compliant version of the snake-board.