Having other kids affect your older ones?

Beebee

Saw this video about the negative reaction of kids after the parents announcing the pregnancy. One instance was kids of 6 ranging from 8-18 and the other one having nr. 3 as the older girl of maybe 6 started crying.

So you think having many kids is selfish for the parents since most of the time the older ones have to be babysitters and or 2nd parents to the young ones?

Or what can benefit from it?