Under CA law (and the law of all states), if the children are the legal children of any of the adults listed on the lease as tenants then you have no right to exclude those children from living at the place whether they were disclosed to you or not in writing or verbally before or during the tenancy. The only way that you can refuse to permit an adult with a child from living in a house that you own is if it is a 1-4 family dwelling and you are living in one of the units (our US Supreme Court has found that a property owner is free to decide who can and cannot live in the same dwelling house with the property owner himself because it is a "freedom of association" issue under the US Constitution). However, any of the adults who are living in the house/unit who are not listed on the lease as tenants are a violation of the lease terms and this situation does rise to a clear cut breach of the lease that you have with the 3 adults who actually signed the lease document. Under these circumstances and under CA law, if they are current on their rent then you can still cancel their lease agreement and ask them to leave -- but you have to send them a Notice to Quit for breach of the lease agreement and in that written document you must give them 30 days to leave the apartment for the breach of the lease -- in the letter to them you must state what they did to violate the lease agreement (they have adults occupying the house with them who were not signatories to the original lease agreement and as such, they have breached the lease agreement and you are within your rights to terminate the lease). There are many online websites where you can actually get a form Notice to Quit that you can use under these circumstances (you can do a search for California Notice to Quit Breach of Lease or variations on those terms and you will come up with many forms that you can choose the best one for your purposes and simply alter it with their names and what the breach of the lease actually is). You must send this notice via US mail and post it at the property in a conspicuous place (or you can simply have the Sheriff serve it for fifty dollars and then the Sheriff will give you a written certification that the notice was served within the terms of CA law and the court will accept the Sheriffs certification without any further inquiry -- I typically recommend using the Sheriff because tenants always try to claim that you did not send the notice or that it was not sent correctly or not posted correctly and sometimes the judges will give them sympathy and make you start the process all over again with a new 30 day notice. With the Sheriff's certification the court will NOT question the service no matter what lies the tenant invents so it is fifty dollars well spent under these circumstances). Here is a pretty good landlord summary for evictions in CA -- http://www.landlord.com/guide_to_eviction_process_ca_summary.htm
When the tenants get to the 31st day and have not moved from the house then you can sign the matter up in your local county district court for a Summary Process (eviction) procedure and the court will set a hearing date about 2-3 weeks after you apply for the hearing and the court will send the summons to you and the tenants. The court will then grant the tenant anywhere from 7-30 days to vacate the house and they are still obligated to pay the rent while they live at the house. Here is a link to the CA court system eviction section where you can get information and forms for use statewide in CA -- http://www.courts.ca.gov/selfhelp-eviction.htm
I hope all of that helps!
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