There are some good recommendations on this site, including a couple of links to family friendly wineries and breweries:
Something my husband and I often do when we go to Margaret River is a trip to The Berry Farm. It's a place that has lots of tasty things to sample and buy like jam and port. The adjoining cafe is a really pretty spot to have morning tea. We'll share a plate of scones and the forest birds always come in to eat the crumbs right in front of us. There's a playground for the kids, too.
Depending on which direction you're coming from, you'll most likely access The Berry Farm via Rosa Brook Road. On the corner of Bussell Hwy and Rosa Brook Road is a small cluster of shops: Yahava Koffeeworks, Temper Temper Chocolate, and Vasse Virgin Olive Oil. Vasse Virgin sells really delicious olive oil products as well as soaps and beauty products. All three places offer a lot of free samples so you can try before you buy. We never need lunch afterwards, but we always buy something to make sure they stay in business! 😉Edited: 17 November 2017, 06:31
Paddle amonst the rocky pools at the south end of beautiful Bunker Bay via Farm Break Rd, climb the Cape Leeuwin lighthouse, watch surfers at Yallingup, order a light meal and share it under the trees at historic art-deco Caves House while watching the bright green 28 parrots.
Lots of ideas here: