Just a friendly FYI before you spend your $$$ that it sounds like toddlers might not weigh enough to have them work properly.
Example this review on ToysRUs:
A big rip off. My daughter was so excited when we got these for her through another retailer. That soon turned to crying when no matter how hard she stomped, she could not get the eyes to lift up. I tried to make the eyes lift by squeezing the slipper but I could not even get the mechanism to "inflate" to the point where they would have popped up. If you go to their website, you cannot even get a phone number to speak to a human about their product. Took the unicorns back to the store and they let me try all of the other varieties they had, but none of those would work well either. So, unless you plan on sewing the eyes permanently up, don't waste the money for these.
Amazon:
These slippers must be stomped very hard for them to open. My graddaughter is too light to open the eyes without stomping with all her might and possibly hurting herself. Better for kids over 7 or 8. or kids that are heavy
My six year old wanted these so bad so we got them for is birthday. They are not worth the money that I spent. They look really cute but don't always work. The eye is very hard to get to pop up. My son does not weigh enough to have them work right. I have to stomp hard to get them to work.
There's even a "Boycott Stompeez" FB page:
http://www.facebook.com/pages/Boycott-Stompeez/213163362098882
