DD (3yo) has had a couple of UTI's as a 2yo....

we found she was very miserable, lethargic and had a temp.
she generally didnt have other cold symptoms (runny nose, cough etc)

to get a sample, you can get little bags that stick onto their bottoms and when the pee, it will catch the sample, they only needed a tiny amount to test DD when we had taken her to the RCH, they then did a catheter to get a better sample to find out exactly what was up.

we pumped DD full of water and gastrolite and she had antibiotics and vinegar in her bath water, my nan told me about that!