This is a simple Baby Care and Wash set up I did recently for my 19 month old and 3.5 year old. This is what I used:

1. Book is Tubbie Time by Kathy Ireland
2. Babies and facial brush purchased at Dollar Tree
3. The pink baby bottles, plate, bib and other items were already on hand and from Melissa and Doug. You can find that here.
4. Wash bowl is one of our dishes I filled with soap and water along with a dish towel they could use to clean their babies.

I like to track how long they choose to play with different set ups.  They nicely played with one another for about 20 minutes before my son was off to other things.  My daughter lost some focus with the babies and went a little crazy with the water and soap all over the house!  She eventually came back to her babies.