Pregnant woman tells 6-year-old nephew that her baby is in her uterus and not her 'tummy.' AITA?

"AITA for telling my nephew that my baby is in my uterus and not my tummy?"

31F. I’m married to my husband Paul (33M) and am six months pregnant with our baby girl. I am Jewish, but it was more of a cultural thing for my family. In contrast, Paul was raised in a strict, Christian family. He told me that when he was a kid, he knew nothing about his body and thought babies came from the stork.

This was very different from how I was raised, but I never put much thought into it. Paul is no longer religious, and we have similar values and ideas about how we want to raise our children. Paul’s older sister Katherine is still extremely religious. She is very involved with her church and is raising her two children (6M and 4M) Christian.

Katherine’s oldest son Tommy came over to my home for a “play date” with me and Paul yesterday. My nephew is a curious, sweet, and happy little boy. I’m noticeably pregnant, and Tommy made a comment about a baby being in my “tummy.” I told him my daughter isn’t in my tummy, but in my uterus. He asked what that is, and I explained it’s the part of a mommy’s body where the baby lives and grows.

Tommy then asked if it’s true that I’m going to “poop out” the baby. I said no, because the baby comes out of my birth canal. He asked what a birth canal is, and I said it’s an opening that leads to the uterus. I also said that humans have different reproductive parts.

Tommy asked me some questions about how the baby got inside of my uterus, and since I didn’t feel comfortable answering that question, I said it’s something to talk to his mommy or daddy about. He seemed okay with my answer, and we continued to play and enjoy our time together.

I want to stress that when I was answering his questions, I wasn’t trying to overstep or expose him to anything major without his mom’s permission. I specifically didn't get into the bird and the bees because I didn't know how his parents wanted to handle that topic.

I truly didn’t think there was anything inappropriate about saying that the baby is in my uterus and that the baby is coming out of me since this is basic anatomy. I didn’t think anymore about my conversation with Tommy until I got an angry call from Katherine this morning.

She said that it wasn’t my place to tell Tommy where babies come from. I was taken aback, and explained that I was just answering his questions and giving him basic information. Katherine thinks Tommy is too young to be having these conversations, and he’s now asking her incessantly about how the baby got in my uterus.

Apparently, Katherine said something about God putting the baby there, but Tommy isn’t satisfied with this answer. I said that when I was around Tommy’s age, my mom explained reproduction to me in very child friendly terms and that it wasn’t too much for me.

I said I’m not a mom yet and so I don’t know the best way to go about the talk, but the way my mom explained worked for me. Katherine said that I have no concept of what’s appropriate for a child and that she doesn’t want to expose him to adult subjects so soon.

I said he’s already been exposed to some extent, considering he goes to church and hears about the Virgin Mary and Jesus coming from her womb. The call ended with Katherine asking me to stop imposing my values on her child and to leave discussions about babies to her. I was confused, because I didn’t think I was imposing any of my values on Tommy.

I told my husband about the conversation, and he is furious. He says there is nothing inappropriate about what I said to Tommy, and there’s no harm in him knowing that the baby is in my uterus and not my stomach. He says Katherine is being ridiculous and judgemental and told me not to worry about it.

I personally don’t think I did anything wrong, but maybe I’m not doing a good enough job seeing things from her perspective. AITA for telling my nephew that the baby is in my uterus and not my stomach? I’d appreciate any advice on how I should proceed with Katherine. Please let me know if I'm missing something here!