In case someone is interested here is an idea that I had concerning this problem. :)
When your sim is about to have a baby, use the cheat "sims.modify_funds +(insert here the value of the retail lot they live on)".
Then copy that lot on the library and place it on their home lot, so that when the baby is born they can move there.
That way they can live with their baby for a few days and they will have the same house and the same funds. It is still better than aging the baby up right away like your sim just gave birth to a fully grown child, which is creepy.
Obviously they will not be able to run the store during the time spent on the home lot though. They can move again once the baby ages up.
So if the store is their only source of income, they better save some money, or they may have to live on quick meals.
If you want to open the store you can still travel there but you won't be able to take care of the baby during that time. Also it is a little strange to go from your house to the exact copy of your house except your baby isn't there.
It still really bothers me that we can't have a baby and run a store at the same time in The Sims 4. I wish that would change in the future.
I know some people hope that the baby-object changes to become a real baby sim that is not attached to a crib.
That would probably put an end to that problem if it ever happened.
