Asking my Fiancé about Starting a Family

How would i go about asking my fiancè about his thoughts on starting a family in the future? . background nonsense; My fiancè (M 26) and I (F 21) have always kind of made jokes about not wanting kids, mostly due to them being expensive, however ever since he proposed he has made more jokes about us being parents or getting me pregnant and I have the genuine confidence to say that he would be a fantastic father. However, i dont know about myself being a mother. I would rather us be married first, because I would like the potential child to have that sliver of security that i didn't have with family, and i want both of us to really work on our mental health (he's honestly doing so much better than myself lately), but he just smiles when we pass families or when a character on one of our shows we rewatch has their baby and he just rubs my stomach in such a way I've seen people do to those who are pregnant and idk. I want to bring it up, but im also so so so scared to because I dont want him to think im trying to rush our future when haven't even begun, but I want to know what he wants or sees in the future for the BOTH of us. if that makes sense. 🥺👉👈 i just know if we worked at it, we may be better than where we came from because even tho my fiancè didnt experience my same trauma and struggles, his family definitely impacted him in a way he wouldn't wish upon his own worst enemy. HOWEVER i also have had 3 miscarriages in the past, one w/ current fiancè, without knowing I've been pregnant and the doctor mentioned my endometriosis potentially being a factor for that happening so im also frightened of us getting our hopes up and then not being able to conceive one, or have the ability to adopt.