u can go to vedanthangal, or any theme park.

You can plan for Yelagiri.. its just 4 hours drive from chennai...but its worth staying there overnight... We had been there last week (our son is 14 mths old). There is nothing to see in Yelagiri except for the lake and murugan temple but just relax. The hotel we stayed has lot of landscape and my son enjoyed the trip a lot.

 u can go to any resort and stay till evening...u'll have swimming pool, lots of indoor games, good food, children's play area etc

you can try the MGM beach resort or the Fisherman's cove..

In OMR road if u go for a drive, u can go to Muttu kaadu lake ,Dakshin chitra,Thiruninravoor temple.....

Vedanthangal ,Mahabalipuram,Pondicherry,Yelagiri..

Thanks Mom , got an idea for this weekend :)