Imagine your OTP discussing the possibility of having children.

Adoption counts too.

This is a serious subject and a serious conversation to have in any relationship, so while you're definitely welcome to take a cute and fluffy approach to it, please don't feel like you're barred from the prompt if your OTP's situation is that this talk wouldn't be, or would be far from fluffy. This includes if your OTP decides that having or adopting kids would not be a good decision for them for any reason, as there are many valid reasons not to and relationships w/o children are as important and valid as those with.

tl;dr the prompt is about having the talk, fluffiness and the OTP deciding that they want kids are optional.