I ended up running to Iron Pony this morning since I live right around the corner. I was able to find a youth helmet, and women's jacket and gloves for the kids. The jacket and gloves are a bit large, but they'll be able to grow into it. I bought fairly cheap stuff on clearance. I got the helmet, jacket and gloves for just under $100. I'd like to go back with the taller kid to see if I can fit her into some offroad dirtbike over pant with pads since they seem to have youth sizes. As for boots, I'll try to find an alternative since they both have different shoe sizes.
Fortunately, right now, they both have the same head size, so they helmet is a solid fit.