Syntheogen - A very good DAW for almost nothing with a lot of aspects to it that you do not find in any of the other bigger apps...
SynprezFM 2 - One of the best synthesizers for Android- Do think that this is the most advanced FM Synthesizer that exists for Android and it is for free!
Music Box Composer - Yes the great music box app for Android. Not only a sequencer with good music box sound but also made for creating paper strips to be used in physical music boxes...
Now it can import midi so finally you can get a children friendly version of your songs with a simple midi import!