Daycare, Illness, and Probiotics

My daughter has started attending a daycare centre and has already had three bouts of flu-like symptoms in as many weeks. Of course, I did expect that this would happen. She's now exposed to more kids and they all play closely together in an enclosed space for hours at a time.
The center does emphasize on hygiene and have extra precautionary measures in place to avoid the spread of illnesses among the children, but the fact remains that, for most children going to daycare, the first few months (the first year for some!) is a trying time for the immune system. Not necessarily bad, as it slowly builds up their bodies' defense mechanisms against bugs.
A friend f mine in Australia gives her child probiotic powder called Daycare Defense, which contains two strains of probiotic bacteria that's supposed to help reduce the frequency and severity of colds and diarrhea in children. I'm trying to look for an equivalent. Can you recommend a brand that has worked for your kids?