Let’s start with a couple of basics.  It might be good to get a bike with a basket for carrying groceries.  Or at least a child’s seat so you can carry a toddler.  It also makes sense to get a small locking wheel in case you want to lock your bike somewhere in a public place, for example.  I don’t have any good examples to share, but there are lots of helpful websites for these things.
assitant
How about things like lights and more bells?
assistant
What are some cool additions to a bike my kids can make?
user