When a child vomits into his trach, post sxn, what can be done to reduce chance of aspiration pneumo?

Prevention. It would be optimal to prevent these occurences altogether if possible; but quick suctioning would be the most immediate remedy. Adequate hydration would also assist the body in preventing this; but if there is still concern, or if a cough/change in breathing pattern develops then seek urgent medical attention!
Suction. Suction to prevent or minimize aspiration.