I saw a price list that stated "Kinder bis 5 Jahre kostenfrei". Is the "bis" in that statement meant to include the year from 5 to 6 years, meaning they go for free until the day before they reach 6 years, or is it meant upto (but not including) 5 years?
The sentence Kinder bis 5 Jahren kostenfrei usually means what @Janka wrote, that is five year old children are the oldest who are free. Nevertheless this sentence is not precise enough in my opinion. To make sure that everyone understands the sentence exactly, one would have to write Kinder bis einschließlich 5 Jahre. Otherwise one will have to pay attention to context related price differentials, for example
Kinder bis 5 Jahren (kosten)frei - children that are 5 years old or younger
Kinder von 6 bis 12 3€ - children that are six, seven, eight, nine, ten, eleven or twelve years old
Jugendliche ab 13 Jahren 5€ - teenagers from 13 to the age of being regarded as adult
Erwachsene 10€ - adults (18 years old or older in Germany, may differ in other countries)
If you see something like that, then the numbers within one line will be inclusive. In case of just the sentence from the question, you might want to ask some person in charge.
Kinder bis 5 Jahre kostenlos
This includes children who are nominally five years old, even if their exact age is 5.996 years.
Kinder bis zur Vollendung des 5. Lebensjahres
The fifth year of living spans from the fourth birthday until one day before the fifth birthday, since Lebensjahr used 1-based counting. Your child of five and a half year does not get anything for free here.
This phrase is often found in the Beförderungsbedingungen des öffentlichen Personennahverkehrs, beautiful German words. :)