Ok is this a parenting fail?

 I might have messed up this parenting thing... Hear me out? My son (6 years old) recently asked me if boys can become girls or girls can become boys. I'm not sure where the question came from (he said his friend told him it was possible, maybe?)

Of course part of me wanted to say no, but I also wanted to add that trans people exist. So I said that it doesn't just happen, but if a man really wants to become a woman he can have an operation. An operation where the doctor can remove male genitals.

Anyway fast forward to today, we're talking about how my son needs to have a mole removed and this involves an operation. And suddenly my three year old girl says "he's going to become a girl, they'll remove his p*nis!" 

Basically we said "operation," and she had heard that there's an operation where boys can become girls (either she overheard me, or my son told her), and she figured that that's what was happening.

Jeez, all I wanted was to answer their questions honestly. Now my daughter is going to be telling her friends that her brother is transitioning?? Omg lord help.