It may be a bit of a drive, but we like Me N' Moms in Ballard. I have consigned and purchased clothes there and had a good experience. They are pretty big and have a good variety of items. We tried Childish Things, but it is much smaller and they are very, very picky about what they buy from you.
Re: Kids consignment stores?
Here's a good list! https://www.redtri.com/eco-savvy-shopping-best-consignment-stores-in-seattle-the-eastside/