Like Sharon said, they're pretty good self regulators. It's pretty normal for toddlers' appetites to vary like crazy. I've learned to just go with the flow...normal kids don't starve themselves, so when Tyler decides to eat nothing but air for a few days, I don't push the issue. Also, with toddler nutrition, it's best to look at it in terms of what they eat over several days because of how much their appetites and preferences vary. If it makes you feel better, you can certainly hold off introducing whole milk until the phase passes, but even if you decided to go ahead with it, he'd probably still be fine (and might even start eating again sooner).
Of course, if it lasts more than a few days or he starts losing weight, that may be cause for concern, but it's usually just a phase!
ETA: Just remembered one more thing...toddlers usually start eating much less around the 1 yr point, so that might have something to do with it too!
