From the G2ss:
Personal Flotation Devices (PFDs)
Properly fitted U.S. Coast Guard-approved personal flotation devices (PFDs) must be worn by all persons engaged in activity on the open water (rowing, canoeing, sailing, boardsailing, motorboating, waterskiing, rafting, tubing, and kayaking).
Only U.S. Coast Guard-approved equipment (types I, II, or III) is acceptable for use in Scouting aquatics. Ski belts are not acceptable. Scouts and unit leaders should learn which type is appropriate for each specific circumstance and how to wear and check for proper fit.
Reference: Safety Afloat, No. 34368 and in the Online Learning Center
Your Class IV PFDS are useful for a comfy seat cushion at the ball park, but I would never take one paddling. I prefer Class III, and I am very happy with my Stohlquist Drifter.