1) Speaking to Person B in a high-pitched, soft, sickly-sweet voice when both individuals are adults
2) Pausing and smiling ingratiatingly sidelong at Person B after every few sentences, the way you do to a toddler; an "aww, isn't Person B cuuuute" kind of thing
3) Always asking Person B how their finances are doing, how their relationships or job are doing, which carries the faint, deliberate implication Person B must be doing badly all the time
4) Always offering (within earshot of others) to aid Person B financially or with advice, when Person B has never asked for such help
5) Saying "OHHHH! Isn't that NICE!" or "Isn't that SWEET!" after Person B mentions something good that has happened for them recently
"Enchildifying in action" is almost invisible to men, but a high warfare art among women. Women sometimes enchildify other women if the second group of women have not had babies yet or choose to be single. This is most marked in African-American, Jewish and Mediterranean cultures. The reason men do not enchildify each other is because a man would beat another man severely if he tried it. It is a way of marking territory, a way of Person A declaring themselves bigger and badder than Person B, and of making Person B "one-down" in front of other women.
"Don't baby-talk and enchildify me, Lydia, just because I run a successful movie company and you just live off your husband and have babies. OK?"
"Of course I have a bank account, you twat. Don't most adults? Don't fucking enchildify me. I see through you."