18mo som, been vomiting 1x a day last few days. no behavior change. what is concerning me, is he brings up bits of clearly identifiable food eaten 8-10 hours ago that show no signs of any digestion.

Time to see an MD: Your concern is valid. Your son either has decreased bowel motility, an infection or partial bowel obstruction amongst other maladies. Vomiting undigested food for a day or two might be okay, but several days in a row requires visit to MD. Some things are easier to repair sooner rather than later. Might be benign or might be serious. Don't wait and see. Trust your instincts.