I used to think that if you had twins that it would happen if you were pregnant (like in early pregnacy) then you would have sex again then u would have 2 sperms and 2 eggs so that would make twins.
A childhood belief about sex

others believed things like this
- i always thought twins had the same name as each other— Elle
- i believed if you had sex twice in a row you would have twins— dona
- I used to believe that twins were always identical.Anon
- My friend used to think that having a threesome would mean you would have twins.— Yank
- i used to believe i would 'catch up' to my big brother one day and we'd be twins.— lil' sis
- That you could give birth to what ever you chose (i.e a girl, a boy, twins, triplets)— Krista Durling