K.V.
Here are a few options:
*Frankenmuth - fun things to see and do
*Huckelberry Railroad
*Local beaches / waterparks
*Detroit Science Center - they have this new attraction "Kids Town" that is AWESOME (it's like a little town - firehouse; stage with dress up things; library; water feature they can put their hands in; vet clinic where they can pretend to be vets; sport room with balls; diner with a kitchen so they can make mommy & daddy food; art room, etc) - obviously your 7 week old is too young, but your 2 year old would probably love it! (My husband, my 2 year old and I got in for under $15 - they have other attractions that cost extra, but this was enough for us and my son loved it!) I can't rave on this enough....
*go to a local bounce house
*Peach Festival in Romeo is this weekend
*Go to the park (either a park or even an elementary school playground)
*Yates Cider Mill
*Bake cookies together
*Halloween costume shopping :)
I know I have other ideas, I just can't think!
www.events.detnews.com usually shows a variety of things available to do in the area (festivals, local events, games, concerts, movies in the park, etc - search by area, what you want to do, date...)
Have fun! I'm looking forward to reading other responses, too, for some ideas!