Thanks for the feedback and the ammunition, everyone. My case now rests.
I seem to have sparked an interesting discussion!
The only times I have used a touch-pad in preference to a mouse was when on a plane sitting beside a generously-sized fellow passenger, when I had no elbow-room.
Anyway, I've just bought this little guy from Amazon. Little hands can fit around it.
The four-year-old, who doesn't know left from right, recognises the differently-coloured buttons.