I think to keep the fire going you both need to do things that ignite the fire in you both, like excitement etc. try to feel like an Teenager again and explore the possibilities . That is my take 
But how can this be possible if you are raising Kids? how can you make things like a teenager when you have to feed, cook ,wash and bring to school your children?
i think this will be applicable for those who are in Mature married life meaning at least 15 and up years of being married?