You can get them from the chemist - but i would be very careful using them on a baby so young.

DS used to cry for like 2 mins after an injection and then stop. I would be more tempted to think about numbing patches on a 4 year old, mainly for the placebo affect.

I was also told not to give panadol before injections for the same reason as Rach said. And quite often they don't need anything but a hug or a feed anyway, so i would rather not be giving my little baby panadol when he doesn't need it.