It depends on your age. If you're 78 you don't want to be caught with a 16 year old. Well what goes on the yacht stays on the yacht
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I would say it is more down to respecting her priorities. Her kid(s) will always come first and it's probably not a good idea for you to discipline them. Understand she's not looking for a dad. Stay clear of any drama with her ex if he is still on the scene. If he is I wouldn't touch her with a barge pole unless drama is your thing. The rest is basics of being trustworthy, supporting her and, always paying the check in the restaurant.
On a side note the average age of a single mom is 38. Apparently many men in their 20's go for a single mom in her 30's.