On page 11 of A Member's Guide to Temple and Family History Work, it states "If you don't know the exact place where an event happened, provide an assumed location, if possible....You may...estimate dates and places if exact information is not available." I use the parents' residence place as the birth place of the children, if there is no other way of documenting the birth place. Prior to the advent of birth registration, there is often no way of documenting a birth place with complete certainty. In the US, a county of birth is sufficient, but a city, town or township is better whenever possible. If you will feel better, you can always preceed the assumed place with "of" as "of Indianapolis, Marion, IN", which clearly establishes that it is an assumed place.