Is my lease valid if my landlord let me move into the residence and it had a roach problem?

Your lease is valid, but in every lease there is an implied warranty of habitability, which requires the landlord to maintain the premises in a habitable condition by complying with local and state housing codes.  When there is a breach of the implied warranty of habitability, the tenant notifies the landlord as you have done and the landlord is required to respond within a reasonable time by making the necessary repairs.  When the landlord fails to respond within a reasonable time, the tenant has the following options:  The tenant can make the repairs (in your case contact an exterminator) and deduct the cost from the rent or the tenant can move out and terminate the obligation to pay rent for the balance of the term of  the lease or if the tenant stays on the premises, the tenant can withhold rent and defend against eviction.  Another alternative is to sue the landlord for breach of the implied warranty of habitability.  Since your son is ill from the roaches, you can argue that this is a health and safety issue which constitutes a breach of the implied warranty of habitability.  You might also want to contact your local housing code inspector, who can bring an enforcement action against the landlord for code violations.