Nothing of real concern as kids will get sick frequently, especially once they are out playing and mixing with other kids, and especially true when they start schooling. For my kid, she was playing at the Kidzworld Wetplay last Saturday. The water was not clean and it was murky white (I have no idea what could have caused the discoloration). I can't imagine how dirty the water was. I can only bet that the water must have been the result of kids (or parents) passing water, spitting saliva, emptying runny nose, and other more (which is not unusual). I can bet that the water is just full of waste from kids or parents who were not feeling well. If the water is not properly sanitized (e.g. with salt or chlorine), you can bet that some kids will get sick after playing in it.
Sure enough, my daughter fell sick after two days playing in the water. She contracted fever and had ulceration in her mouth, suggesting that it could be viral infection. Her throat was not yet sore. Her temperature reached 38.6 degree Celsius. We couldn't do anything except to reduce the fever by medication. The rest would require her own immune system to acquire the immunity against whatever was/were assaulting her system. Poor kid. I guess it's part of her growing up process, i.e. to be exposed to as many pathogens as possible so that she will grow up to be stronger.
Anyway, I really hope that Singapore Zoo will be mindful of the poor quality of water at their Wetplay area and do something about it. Having viruses originated from other kids are not really bad (well except for the hand, foot and mouth, HFM caused by coxsackie A virus). I'm not sure if HFM virus is transmissible by dirty wetplay water or not (especially considering that viruses tend to die very quickly outside the host/vector).