They will get up set because you were doing it before and now won't do it because of the baby. So decide what you want to do with the older child when you go home and do it from day one. You can do different things when you are holding the baby verses holding the baby. Dad may do different things than Mommy. It is when we stop doing something with our child that upsets them.
Regressive symptoms can occur but there are two categories.
There is the true retarded regressive symptoms like wetting their pants after being dry, refuse to eat and be spoon fed, or suck on the breast or bottle again. They will crawl on the floor or talk a little baby talk or try to climb in the crib again. You will see them play mommy or daddy and spank their dolly or teddy bear. They are role playing the adult and this is healthy. You usually do not punish them for doing that.