Well you can create apps on various softwares.A few to be named are scratch, hopscotch(this is an app),flash,HTML& Python. I would recommend using Scratch and Hopscotch as they are quite similar to each other and are very easy. Personally I am more inclined towards scratch as I myself am a scratcher and have mace quite a few games.Hope any of this comes useful
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Dheeraj
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Sri Sri Ravishankar Vidya Mandir, Bangalore