Almost all critically ill children who are mechanically ventilated require sedation and analgesia. Providing effective sedation for children in the PICU requires careful balancing of the need for sedation with the adverse effects associated with sedative medications. Clonidine is often used as an adjunctive sedative and analgesic in children but a well designed and adequately powered randomized trial is required to test the effect of clonidine-based sedation. Because there are no large randomized trials of sedation related interventions among critically ill children there are many unknown factors. This pilot trial, focussing on feasibility outcomes will assess the feasibility of, and inform the design of, a larger randomized controlled trial which will focus on clinically important outcomes.