Go to www.identi-tape.com and peruse the various flavors of reflective tape, conspicuity tape, etc. In particular, look for the "vest trim", which is essentially a wide hi-vis colored ribbon with a reflective stripe. Between that and the various other kinds of reflective and hi-vis tape they carry, you can either make what safety gear you need or stick reflective or hi-vis material onto whatever stuff your kids already wear. If they're into projects, you can even make a project out of it. If they're the types to object to wearing a dorky DOT vest, maybe they'll object less if it's something they made themselves.
Dunno if the OP is still looking or not, but I popped into the Dollar General that was built not too far from my house. They had some "Open Trail" branded hi-viz yellow and safety orange vests with reflective trim for $3. Packaging stated that the product in "not rated", so I'm guessing that it doesn't meet ANSI or DOT specs.
"If I ride, I will know the way the trees smell after the rain... My breath will fill the air instead of smoke and car exhaust... Road rage will turn into laughter and I won't be a boy or a girl, I will just be a rider...and the planet will cool down and survive and thank me for riding with flowers & glaciers & fireflies & snow days off from school... I will be strong... I will only use oil in my chains and oil tankers will haul chocolate milk" by People for Bikes http://www.peopleforbikes.org/