We are considering going on a cruise this summer with our 2 kids who are under age 6, if we can find a good deal. We thought about paying for my mom to go along. She has never gone on a cruise but it is not my dad's thing so we think she would love to go. We thought it would be good to have someone to stay with the kids while we went out after bedtime. We wouldn't do that every night. We get along great with her, the kids love her, we have traveled with her before so it should go well. We would also get her her own cabin.
Let's play devils advocate and tell me the reasons why this is not a good idea.