Or just babywear both girls to work/class and if anyone asks you about them, you can say they are:-

1. your imaginary friends;
2. growths;
3. a figment of the other person's imagination;
4. your newfangled dictaphone;
5. the Doctor;
6. your contraceptive device;
7. spies;
8. a matter of national security;
9. your mastitis prevention strategy; and/or
10. your bad pick up line avoidance technique.

You could also say they are a parasite (according to House MD), lunch, abnormal growth (I wouldn't say cancer ... that's a bit harsh), your husband's sperm which stuck around, or a few other things, but the above are probably the more socially acceptable responses.

Go on.

I dare you.