He probably just has an icky tummy..... Cheerios should be fine... but I use them as treats rather than a meal. I would definitely do something bland like the chicken and rice..... then you should find a kibble that he will eat and stick to it.... I went through about 4 different ones, before I finally settled with ACANA. He gobbles that right down.
Just be Careful with what kind of human food and how much because it can cause Pancreatitis which from what I have heard and read is No Fun!!
Hoping your baby feels better Soon!!