Is tenant responsible to pay if the agreement was not renewed

I was living in rented flat for 3 years. I have vacant the flat 45 days ago. I was living with my wife and 2 year son. During this 3 years period my son written on three walls of flat with color wax pencil. Now landlord call me and demand for money for paint that paint. And giving reason that your 2 years son written on the wall. At time when I was shifted into the flat a rent agreement was signed by both the party. During this 3 years tenure the agreement was not renewed. Also landlord never did whitewash during the period. In the rent agreement he has given in the first year which has expired, it was mentioned "lessee shall not cause any damage to the said premises and in case any damage is caused the said premises by the lessee, the lessee shall be responsible for the same and the lessee with liable to restore the same in its original condition or pay cost thereof, except normal wear and tear". Flat already white washed by the landlord this week. Please suggest what I should do?