Vacant Seating

My wife and I are taking our 3 oldest sons - ages 10, 8, and 5 to the noon game this Thursday vs the A's. I haven't purchased tickets yet, but the boys are going to want to be in a seat that either gives them a chance at snagging a foul ball or a home run ball. Do you expect I'd have any issues just buying the 5 cheapest tickets I can in the 400s and then moving to one of the thousands of vacant areas of the ballpark after game start? If I look on ballpark app, nearly all of LF and RF are still unsold, as well as many parts of the upper rows of sections 128-131 behind the dugout.