D.B.
Hi K..
There are tons of things to do. Have your oldest son in charge of reading a daily story to your little ones, having them sit on either side of him so they can see the pictures, too. My son couldn't read fluently at 4 but was able to "read" by reading the pictures (make up his own story). When my daughter reads to my boys (9yrs, 5yrs, 2.5yrs), they just listen and stare at her. They are so mesmerized by her. My 5 yr old is able to read, now, so when he reads to his baby brother, it is the cutest thing because the stories are not as complex as the stories my daughter reads to them.
Another suggestion would be to have your oldest help you decide what your little ones will be wearing that day. He can also be in charge of making sure that his baby brother has his favorite toy before leaving the house.
I have sooooo many suggestions, but I think if you just involve him in other aspects of his baby brother, he'll be bonding and being a wonderful big brother. As far as playing, you can have him sing the alphabet and count numbers to him.
Take Care!
D.