I would suggest visiting at the night time as you will be amazed to see the roses made of LED lights lighting up like a flowing river made out of candles.
You can visit the Kakao Talk store where you can buy few cute souvenirs for your kids or for yourself :)
There is a coffee shop in the DDP so I enjoyed a hot sip of cafe late to conquer the cold winter month of the December.
There is no ticket needed to click DDP photos or visit the LED garden, this makes this place a worth of a quick visit for few awesome photos.
I hope you visit Seoul and enjoy this place too.