Gosh - such a long time since I posted! And now I only have my latest socks to show you...
I have created the pattern for these myself, although I'm not sure it's quite right yet! I made turquoise-blue ones first (birth to 3 months size) and did the heel I normally do on my own socks.
However, it is not necessary to have a reinforced heel on a baby's sock as it will not be rubbing on any shoes, so the next one I made I simply did moss stitch to define the heel...
...and I think it works out quite well. I've tried them both on little babies who just happened to be at the knitting groups I was attending at the time and they do seem to fit quite nicely.
The pink pair are in the 3 - 6 months size and I think you can see the size differences in the pictures.
When I've worked out a couple more sizes I'll publish the pattern on Ravelry, but that might be a few weeks away yet. I used mini-balls of Regia which were £1.99 a 25g ball.
There was a little left over from the ball after the socks were finished but I'm not sure you could get a whole extra pair out of the remainder if you made 4 pairs from 1 100g ball.