In the same vein as comfortable clothes, you'll also need a lot of casual clothes. Being a mom means baby food splotches on your pants and spit-up on your shoulder. It means your sleeve sometimes acts a tissue.
So, put the brand-label, "dry clean only" outfits back in the closet and save them for a childfree night out. You paid good money for those clothes, so take good care of them. For day-to-day mom life, go more casual. Think jeans, cotton shirts, sportswear and casual sweaters. Find some cute, comfortable flats that go with everything. Remember, being overdressed can be as big a fashion faux pas as being underdressed.
A good way to decide what to wear? Before you choose an outfit for the latest birthday party, think, "How upset will I be if this gets stained?"