Does anyone know how the Prop 19 parent-child exclusion applies to multi-unit properties.

While I live almost as far from you as the contiguous 48 states will allow (Olympia , Wa), I have a "stray child" of a house just down the street from you in Sebring!  

Worst case scenario, they have the tenant pay the full year lease in cash in advance, at the very minimum 3 months upfront (on top of the deposit and 1st month).You're the landlord in this situation so it's your decision to make but it's going to be extremely difficult getting people across the world to pay back rent for their child should the situation go south at all.

Hey everyone, I recently moved to Charlotte with my wife and newborn daughter. 

Our lease has a clause limiting the duration of guest stays in any year and spells out the additional rent for staying beyond that limit.However, if the tenant had a new child and their parents were coming to help with the transition, I would be reasonably accommodating.  6 months might push my desire to be accommodating, but for a good tenant I would let it slide.If I found out as late in the guest stay as you have, I would discuss the need for better communication and call it an opportunity to educate the tenant on my expectations.Good luck

However, their child / the IRA account holder's spouse is a disqualified person to the IRA.  

Prop 19 gets rid of the parent-child exclusion in a huge way that will hurt long term real estate investors. 

They call this the parent-child (intergenerational) transfer exclusion. 

to the second question.Once the child/ren moves out, it will get reassessed.

The parent to child transfer of property tax base, was changed this year, due to Prop 19.