Emaze is a similar presentation platform to Prezi:

• Your presentations are publicly available to anyone and everyone if you have a free account
• If you have an educational institution e-mail account you can get a teacher account for free (within which you can make your presentations private)

However, the options for your presentation are a little bit different:

• Your slides appear more as a traditional linear powerpoint (instead of in a larger non-linear poster format)
• You can add more image clips and sound clips to your slides – which might be better for an elementary audience (like here)

I also found a website where some teachers gave reviews of Emaze.