If my landlord failed to infrom me of lead based paints in my home and my child has been affected, can I sue him?

You could sue the landlord for the dangerous condition on the premises which caused injury to your child.  You will need to be appointed guardian ad litem to file a lawsuit on behalf of your child if your child is a minor.

Prior to filing the lawsuit against the landlord, it may be possible to settle the case with the landlord's insurance carrier (homeowner's insurance).  When your child completes his/her medical treatment and is released by the doctor or is declared by the doctor to be permanent and stationary which means having reached a point in medical treatment where no further improvement is anticipated, obtain your child's medical bills and medical reports.  Your child's claim filed with the landlord's insurance carrier should include these items.  Compensation for the medical bills is straight reimbursement.  The medical reports will document the nature and extent of your child's injuries and will be used to determine compensation for pain and suffering, which is an amount in addition to the medical bills.  If the case is settled with the landlord's insurance carrier, NO lawsuit is filed.  If you are dissatisfied with settlement offers from the landlord's insurance carrier, reject the settlement offers and file your lawsuit against the landlord based on premises liability (the dangerous condition on the premises).  If the case is NOT settled with the landlord's insurance carrier, you will need to file the lawsuit on behalf of your child prior to the expiration of the applicable statute of limitations or your child will lose his/her rights in the matter forever.