Actually.....50% of it (at least ...at this point) has nothing to do with preK. It is just an old-fashioned money grab. But this is probably out of the scope of eG.
http://www.philly.com/philly/news/politics/20160614_Drink_tax_proposal_had_some_sweetners.html
http://thephiladelphiacitizen.org/soda-tax-philadelphia/