Hi! I am a SAHM too & I use my little girl as a weight
Try laying on your back & bench pressing her (unless she's a drooler like my kid!) As for weights, start with a liter bottle filled with water - that's 2 lbs. Canned food works too, books are good -- I didn't invest in 5 lb dumbbells for the first month or so & now I have 20 lb ones. I do lunges when I have Fiona's bottle in the microwave...I live in downtown St Paul Minnesota & we walk sidewalks all the time. Just make sure you have on shoes with some support. One thing that has helped me is interval training -- walking at a good rate for a minute, then walking as fast as you can (imagine you are rushing to the bathroom or trying to make a bus) for 15-30 seconds. Also, what got me moving 8 months ago was Fiona's "Go! Exercise with the Teletubbies!" video -- we dance all the time to everything from the Tubbies to Barney (gag) to Gnarls Barkley & Fergie...that burns calories too!
The trick is to move...just move! I started out winded after 3 minutes of "Head Shoulders Knees and Toes" and 8 months later, I am able to do a hard hour on the elliptical at level 8 or 10 and get in a minimum of 5 miles!