I'm treating a client's 3 year old daughter next week for the first time, so she'd be my youngest to date - though obviously no results to report back yet.
But i've treated 4 and 5 year olds in a school where I work, and they've reacted beautifully to it. Main results being improved mood and energy levels as well as better peer friendships/emotional wellbeing.
What about yourself Lisadawn?