My friends have all got new phones
No apostrophes - 'friends' and 'phones' are plural nouns
My friends phone is the latest model. (one friend)
friend's phone (el telefono de mi amigo)
My friends phones are all new (lots of friends)
friends' phones ( los telefonos de mis amigos)
Those are the childrens shoes
children's - the shoes belong to the children
This shop sells clothes
No apostrophes - 'clothes' is a plural noun
Here is the principals office.
principal's office (oficina de la directora)
Yesterday I bought some new shoes.
No apostrophe - 'shoes' is a plural noun
That is Amys bag
Amy's bag = la bolsa de Amy
That is my parents house
my parents' house - la casa de mis padres
He is 6 years old
No apostrophe - 'years' is a plural noun