Discrimination laws apply, so care should be taken to comply.
Expect a higher level of legally allowable and actual wear'n'tear with younger kids or more kids.
If you plan to rent to a family of 7, ensure the property is robust, big HWS, plenty storage (shed?), installed water meter so tenant pays big water bill not you, big clothesline, remove any sharp edges and dangerous items, make sure the fencing is ok, check the electrical stuff, be ready with your pet policy.
Rent should be adjusted to cover the higher wear'ntear if you have say 5 kids compared with none or one, but you can't tell them the reason is because they have kids not adults (discrimination).
Allowing sufficient space and bedroom area per person (child) will create a quality environment thereby encouraging civilised use of the property, providing you have good tenants.
A landlord in NSW can't demand or insist on more than 4 week's rent as a bond for unfurnished premises. But as a PM, I have suggested to prospective tenants, who tell me that it's not easy finding a home for 7, that a property owner would understandably be impressed with an applicant who offered some extra bond. It is not required of course, but offering it may help.
cheers
crest133