Explaining to my 5 yr old about babies...

My 5 yr old is very curious about how the baby got in and how it will get out I told him that daddy planted a seed and it is growing into a baby and when time comes the baby comes out of my tummy (although I plan on another natural delivery) anyone else having trouble explaining to their lil ones any advice I don't want to tell him the truth obviously but my Gramma says that's how she handled it with my mom when she was pregnant with my uncle but my mom (then 3) used that awesome kid memory to explain to everyone around how her brother was made... I don't want to send my son to kindergarten for him to give his class mates a sex ed lesson lol