There is certainly a time and place for following rules and learning strategy. When two of the players are age 3 and under is not that time. Nope. That's the time for "I'm green" and "I'm the pretty red." A time for counting squares and making things up. Maybe the older sibling directs the action - or maybe not. It's a time for parents to just "step away from the game board" and let the game run itself.
When kids make up their own rules, board games become a playground for role playing and creative minds.