Our two are 2 and 4. I'm dead against the youngest having one, and I'm really reluctant to let the oldest have one either. Mr P thinks I'm being psycho-mum again.
They would each be with one of us parents, and we would basically be holding their hand holding the sparkler, but I'm still quite nervous about it.
My answer was random and would see the previous suggestions make a lot of sense but if it's OK for a supervised child of 3 or 4 why on earth are they now banned at all public firework displays?
If the sparkler is lit by an adult holding it and then placed in the hand of the toddler whose hand is then held to draw shapes and write their name in the dark a I think there is very little risk.
If I wanted to be particularly anal about the whole scenario I would suggest having a bucket of water to one side to extinguish and cool the the dead sparklers.
I loved sparklers and still have to write my name with one :-)
I personally don't think I would let my kids have them at all. I am a firm believer that fireworks should be at organised events only. Sparklers can be so dangerous.