Advice needed: age appropriate stranger danger conversations

I am looking for some advice on how to talk to my 3 year old about stranger danger in an age appropriate way. My 3.5 year old daughter has always been incredibly outgoing and warms up quickly. She loves making conversation and truly she has “never met a stranger”. This has always worried me and I try to emphasize trustworthy adult behavior and I label strangers versus friends as appropriate.

An incident happened today that has made me sick to my stomach and has made me extra worried for my daughter’s wellbeing. Especially people whom she kind of knows (or recognizes). Before reading please know that I will not be contacting this babysitter again and a stern conversation about safety has been had.

Today was the first time we trialed a babysitter. Ever. My daughter has never had someone outside of our immediate family look after her. And our immediate family members have only watched her a handful of times throughout her life. It’s really just been her dad and I. The babysitter hung out in our home for about an hour while I did chores around the house. I needed to do yard work so I suggested that they go to a large grass area that is visible from our front yard (although I was in and out of the garage/ front yard). It is essentially our townhome’s communal outdoor space. We frequent it often. At one point during my weeding, I looked up and noticed that my daughter was out of sight but the babysitter was still sitting in the grass. As I walked over, my daughter was coming out of the front yard of a nearby neighbor’s home. Apparently, the neighbor noticed her runny nose and had her come along to her home to grab a few tissues. The babysitter had a severe lack of judgment by allowing her to do so. To say I was livid was an understatement. It took me almost 3 years to start to put trust in a sitter, only to have it broken within the first few hours. I’m disappointed in the sitter, the neighbor and myself.

I’m trying to learn from this and the main way I think I can is by reaching out to fellow moms for age appropriate ways to talk about strangers with my kids. This neighbor is a 70 year old woman who will often come talk with me while my kids are playing. So I’m sure my daughter views her as mommy’s “friend”. But is obviously not the case. But how to describe that nuance to a 3 year old is lost on me. I told her that she needs mommy or daddy with her to go into anyone else’s home. I don’t know if that’s enough.