There are lots of poster to tell the children how to do Wadu, Gushal and make Salah etc.
From the website
''Our objective InshaAllah (by the Will and guidence of Allah) is dedicated to help designing posters, for the purpose of islamic Dawaah and Islamic Education. If you are a member of a Masjid, Mosque, Charity or Dawaah Organisation in any country and you need a English poster to promote an event , then we can help you Inshallaah''.
These poster are free to download and you can print it your self on A4 or A3 paper with almost the same resolution.
You can also buy them online, these are already printed form of the posters which can be used at home masjid or school to educate the kids.
There is a ipad iphone application by them regarding Salah, Wadu and Ghusal etc.
Click here for more details.