My kids are 4 and 2. They hold the baby when sitting - DS can hold her unsupervised but I sit next to DD when she is holding. Neither have ever tried to pick her up otherwise. When she is lying on the floor they both give her cuddles and kisses and lie next to her and talk etc. DS likes to do up the tabs on her nappy. Sometimes I get in the bath with all three of them and hold the baby, they love that.

Other than that they do little jobs to help with her - get a blanket/wipes/nappy/toy.

I guess if you make them sit to hold bubba from day 1 then that is just how it is done, they won't expect any different.