I often found some of my best educators started their journey as volunteers. I found it was beneficial to everyone concerned. Experiencing day to day life in an early years environment can be the best indicator as to whether the role is suitable, as well as giving leaders an opportunity to see someone in action. I could usually tell within a few minutes whether someone was going to be good or not! I actually started advertising for volunteers some of whom became permanent members of staff.
One thing i will say is that it doesn't always work out, and can be time consuming going through the process of registering and sorting a DBS, particularly if they don't come back after one session, but more often than not it was worthwhile.