Personally, I wear slippers all the time, not shoes really. I do home daycare and we keep our house at 68* (drop to 58* overnight)..we like the cold. But after 2 foot surgeries a few years ago, I have nerve damage in my right foot, so have a hard time maintianing my foot temp (can't wiggle it like we noramlly do which keeps it warmer).
I love and wear for 12+ hours a day, Acorn slippers..the Polar Moc ones. They make a few kinds for kids..slipper sock topped ones and the polar moc ones like I wear. Thru Acorn online they are $20...so I would look around online or for local stores who may have sales and coupons and odd sizes or last years color choices on clearance.
I just toss them in the washing machine every so often..they shrink a bit and feel a bit snug for a day or 2, then are fine. I have 2 pairs and this will be my 3rd winter using them (I asked for them for Christmas that year) and they still look almost new! Like I said, I wear them for 12 hour work days plus in the evenings and just wash them every so often!
http://www.acorn.com/categories/kids
I HIGHLY recommend them!!!