You are remembering correctly. St. John the Baptist was rendered sinless while in his mother's womb in the presence of yet-unborn Christ. I believe that to be both Catholic and Orthodox view, however Jo Kus told us it was allowed but not dogmatic view in the Catohlic Church, and Kolokotronis and Kosta can correct me regarding the Orthodox dictrine.
"You are remembering correctly. St. John the Baptist was rendered sinless while in his mother's womb in the presence of yet-unborn Christ. I believe that to be both Catholic and Orthodox view, however Jo Kus told us it was allowed but not dogmatic view in the Catohlic Church, and Kolokotronis and Kosta can correct me regarding the Orthodox dictrine."
I must confess I have never heard of this with +John the Forerunner, but a quick google on the subject indicates that at least among the Russians this is a pious belief, a theologoumenon. There is the interesting idea that although Christ was the only truly sinless person, His sinlessness was completely of His own doing whereas both Panagia and +John the Forerunner were preserved by God from sin because of the special role they each played in the Incarnation. I'm not sure I buy into the latter part of the theory at all, especially with +John the Forerunner.