Want to know if you're kids are sick or not? Give them "The Banana Peel Test".
Step 1. Peel banana.
Step 2. Set aside peel, eat banana.
Step 3. Take peel and give to child.
Step 4. Evaluate.
If the child eats it, with such zest that pieces disappear (only to be found in tomorrow mornings diaper), and long enough that you're able to take several pictures and the child appears to actually be enjoying the experience, the child is sick.
Whereas, if your child takes a bite, gives you a "What are you feeding me this for, it tastes disgusting, can I have a cookie?" look, the child is on the mend.
Needless to say, Max is on the mend, Artemis, not so much...
Disclaimer: This test is known to be 50% accurate.