I think it's an excellent idea what you did with your children because they learned an important lesson while having fun as a family. Although I do not know if the guys hold a full game of Monopoly since the game is very long.
If you had taken the time to explain them verbally or with a blackboard, they would surely have been bored.
A question. Were they aware that these loans violate the rules of the game?
RE: A Parent’s Help Becomes a (Questionable) Monopoly Strategy