And then imagine being asked which one of you got pregnant unintentionally... because you couldn't possibly have planned this, could you? Imagine going for a routine ultrasound with your pregnant daughter as company, and proudly telling her, "Look, it's your little brother/sister!"
You may even go into labor at the same time, and give birth one after the other. Being pregnant at the same time as your child may sound a little extreme, but it happens every now and again and can make for quite a lot of fun. My friend was in her late forties when she got pregnant with her ninth and final baby. Her eldest was already married too, and turned out to be expecting a baby at the same time. My friend's first grandson was born just a few weeks before her youngest daughter. Her baby daughter was born being an aunt!
Unusual, but very funny. This situation can make for some especially personal entertainment if you are ever out with your newest addition and your daughter's baby at the same time. Now, imagine people asking if the cuties are twins, only for you to honestly be able to answer that one is your child, and the other is your grandbaby. You can joke that your grandchild's same-age uncle is babysitting him! Have fun, and use this opportunity to bond with your daughter. You are enjoying one unique bonding opportunity that not many women ever get to experience!