Kids this age don't play in groups. At the most, they will do parallel play, but I think they might even be too young for that.
If you are going to play tapes, start playing the Sounds Like Fun tape by Discovery Toys.
It will just be noise to the kids at this age, but the songs are educational and teach counting to 100, the sounds of the ABCS, all gentle and fun songs. You could play it at naptime. Imagine if a child heard this tape over and over every day. He would know the common sounds of the letters without even trying, and he certainly could "count by tens up to 100", etc.
Kids this age love balls. Just give them several balls to roll back and forth and they will laugh with delight.
Go check out the book, The First Three Years of Life by Burton White. He went into homes to watch infants up to 3 year olds. He has lots of ideas on their development and their preferred pastimes. ISBN #: 0133191788
Also, play a little Mozart or the Vivaldi (the 4 seasons) in the background while the kids play. Now's the time to expose them to the best of the culture.