Hi there,
I had to collect a urine sample from my LO when she was about 4 months old. My GP provided me with a pack which contain some sterile pads (bit like panty liners) which don't absorb the urine very quickly, a syringe and a sample pot. The idea is that you put the pad inside the nappy, and regulary check the nappy, about every 15 minutes (a pain I know) and when the pad looks wet, syringe the urine from the pad, this is easier than it sounds, I promise! Then transfer it into the sample pot.
Maybe you could give your surgery a ring and ask if they supply these?
HTH
Jen x