On most any day you could find people walking dogs, or children playing in the area.

A lawyer might be able to answer this better, but most rentals fall under fair housing laws (there are exceptions) and that protects against discrimination based on familial status which means children or someone who is pregnant.

I really like LLCs compared to corporations because of the free stepped up basis for passing property to my children. 

Their children (now in their late 40s) inherited the house, but they have not listed it on the market, and I heard that neither is willing to move into it from their current setup, so the property has been sitting vacant.

General Partner is elderly fatherb.  12 Limited partners - all children , spouses not included - cheaper by the dozenc.

Replacing a bathtub with a shower can make narrow bathrooms feel larger and more modern.That said, consider keeping at least one bathtub in the building for market appeal, as families with small children or certain renters may prefer it.

I understand it was (allegedly) caused by a kid, but parents must take responsibility for their children's actions.

I lived in a college town and student rentals did very well as did STRs for parents coming in to visit their children.  

We go above and beyond when it comes to protection.. starting with insurance coverage, sings in the listing and in the property that there is no guard on duty (as silly as that sounds), putting extra locking device high enough so youngsters can't reach, an alarm/beep system to alert them that door opens for those with small children (or elderly) so they cannot wander out in the backyard with no one noticing and risk drowning.

Providing relocation assistance to tenants, for example, if I want to sell the property or move back in - this can range from one month's rent to thousands of dollars (e.g tenant has a disability, minor children, elderly it will cost you more), depending on the city.