Swearing

Out 4 year old learned (to my horror) the “f” word from our child neighbor who lives behind us. Our children will talk over the fence and play occasionally. The child over the fence is in the first grade and told my children that his mom uses this word towards him. This made me so sad! The mom and child go to church..the child is in a Catholic school…it seems he is doted on by his mom. She is kind to my children and seems to be sacrificing much for her child..working two jobs just to provide, creating experiences for him, and celebrating life’s occasions with him. There is no dad presence or other siblings. How do I address this? Do I say anything to the mom? My husband told all of our children (including the neighbor child) that this is a word none of them should say and we did limit their time together without our supervision. This is the first time any of our 5 children 10 and under (to my knowledge) have heard this word and our 4 year old will say it when he is not getting his way. We were at the store today and he was tired and he just started saying it repeatedly. We left immediately and I told old him we don’t say that word and it is very hurtful. It’s very difficult for me to not take this personally, and I feel angry that he has heard this word. I’m not sure I handled it correctly because he has not stopped saying the word on occasion. He heard this word maybe 2-3 weeks ago. He has said you “f”… even writing that makes my heart sink. We have tried very intentionally to promote teamwork and respect, and to hear my small child say this is devastating.