Prove using a punnett square that two blue eyed people can not have a brown eyed child

So considering B is for dominant Blue eye and b is for recessive brown eye;

Now the possible combinations which will ensure a blue eyed person will be BB or Bb but never bb.

So using the square for BB and Bb

B B

B BB BB

b Bb Bb

All the above combinations would make all children have blue eyes BUT 2 children would also have brown eye colour as a recessive allele which could effect the next generation.

I can't be 100% sure because of not reading the actual question but this is my best guess.