she's definitely my "grown up" body inspiration--i don't really see it feasible for me to stay thin thin as an adult, especially after kids, given the career I want, the amount of time i'll be busy, etc. She looks really healthy, happy, and fit. Great look overall--and her skin is amazing (in person too, i've been lucky enough to catch a glimpse at whole foods a time or two)
Barring any catastrophic medical mishaps that require bedrest etc you'll probably be fine after you have kids because you're taking care of yourself now. Most of my friends who were body conscious before they had kids looked really good afterwards as well because they didn't gain a ton of weight while they were pregnant and kids are active little things. Most people I know didn't really change much from giving birth; you could have predicted the ones who were likely to stay overweight.
Gwen's always been super body conscious. I remember reading an interview with her in around 1997 where she constantly talked about needing to work out and check her diet. She's actually a lot slimmer now than she was in the 90's; one of the reasons I find her quite inspiring if I'm honest.