Before the age of two, toddlers don't interact or play directly with other children, but that does not mean it is not important for children of this age to play together.  Early on you will see 'solitary play' where children play with toys almost in isolation of the other children around them.  Later, children learn by watching one another and through imitation - this is 'associative play', characterised by playing independentlyand sharing toys and play equipment but still not interacting directly. Only later on do they learn to co-operate through sharing, interacting and taking turns with the same toys, this is 'co-operative' play.  You will observe all of these stages as your baby grows, and they are all a natural part of development and learning.  It is good for your babies to mix with other children from an early age because it exposes them to free play and external influences that you alone may not introduce at home.  Of course, your babies will also learn directly from you, and that's why it is important to spend as much one-on-one time with your children as possible.

Newborn babies have a limited understanding of the world around them. For their first few months, they are experimenting and learning through experience of their environment. Up until 6 - 9 months, babies have no concept that an object exists outside its immediate sight. That is, that if a baby can see a building block then it is there, but if it isn't in sight, then it may as well not exist. Only at around 6 - 9 months does a baby realise that if it drops a block, that the block is still there nearby. At around this time, you may catch your baby purposefully dropping things to see where they go - this is all a part of that early experimenting with their surroundings, trying to make sense of the strange world that they have found themselves in!