To be honest, I am open to all ideas. My childhood, and my children's childhoods, are in the dim and distant past so I am not current on what kids (of any age) like. My own feelings are the subject painting will be there for them at the darkest period of their life so may need to be both happy, interesting and be able raise their spirits just by looking at it. I don't think your paintings have to intricate, just something that they can understand and associate with happier times.
Sounds easy doesn't it. Yeah right....