This is how I imagine fairies: Maximally 1 m in height, female, wearing a dress, shiny and sparkly, flying with animated butterfly wings and a particle effect emitting fairy dust. 

You fairies might be more cute and child like (my fairy - according to my story  - is an architect among the fairies). Fairies suck nectar from flowers and also eat honey.  They love beauty and either live in nature with  a lot of vegetation or in beautiful buildings close to nature.

For a family friendly game I would use things e.g. rocks as enemies instead of persons. The rocks could be obstacles or actively threaten the fairies by falling on them from somewhere. The fairies might use their magic to move rocks or turn them into something nice like flowers or sparkles or butterflies. Fairies can't die but by after colliding with a rock they might have a crash-landing and fall all the way back to the beginning of the level.