I'd say no. Not the valley. I just moved my family to Seattle, same situation. I'd been a freelancer in Kalamazoo and the work had mostly dried up, so I got this huge offer and it seemed too good to pass up. I'm having huge doubts as to whether it was the right decision. SV is twice as expensive, I'd not consider it.
https://news.ycombinator.com/item?id=15082982
Also have you lived in SV before? I did years ago and didn't care for it even as a 20-something. At least WA has no state tax, mountains right next door, and eh, I like the culture better. More real, less flashy, and still has some blue-collar too. I think better for families. If your offer is from a big name, then they've certainly got a Seattle office. I'd inquire about that possibility. And salaries are very close, especially considering the state tax.
But like I suggested, even Seattle is hard to call a slam dunk. If there was more than one crappy company to work for in Kalamazoo I'd have loved to stay. It's cheap, it's a college town so there's stuff to do, has an amazing arts scene for its size, great outdoor activities, good public schools and park/trail system, and a good mix of political views that still talk to each other. I've lived in IN and OH too, and had less affection for those. So I guess a lot of it depends on your current situation too.
But if you've got a decent job with benefits and are living in a place you don't mind, 140K won't get you far in SV. One other quick note: before moving out here I looked at housing prices but didn't realize that the places that were showing up in my budget were all horrible school districts, so if you think you're seeing some nearly-affordable options, cross-reference the school guides.