Well i have 3 children.(3,5,6) I usually take one child with me to my dr's app. Then get them a snack afterwards. Usually its a 30 minute wait(depending on how busy they are) and I usually bring paper and pens and draw pictures or whatever with them while were in the waiting room.Or read books if they have any.
Usually some nights one will wake up and i'll put them in bed with me and cuddle with them.Or one will wake up and will sit on the couch and cuddle and watch tv with me.
MOSTLY we do take them all together some where. I take all 3 to the park together.or a store.
If one child is sick usually i pack that child in to their dr by themselves and hold and love them; giving them that one and one time.
There is ways to have one on one time without spending money or going anywhere.
I think children will always feel or be jealous no matter what. My kids can have the same toy and one will start crying saying there toy isn't the same as the others.