Hi J.,
I have been a preschool director for several years and before that I worked at various daycare centers for many years. Every child is different and all children enjoy interacting with other children, but as soon as you place your child in a situation where they are around other children you will find they amount of illnesses your child will experience will increase dramatically. (Sometimes 2 to 3xs more frequent colds). Now, this is true no matter where your child attends and will happen whether you wait until kindergarten or not, so I wouldn't let this be a deciding factor.
However; I will tell you what I've told all my preschool families, I recommend waiting until a child is three years old before enrolling them in a preschool program, and this is why:
1. Developmentally, by three most children have moved into a stage of development where that begin to play cooperatively, prior to three children play inwhat is called "side-by-side" play, which means they are in close proximity of one another, using the same materials, even doing the same things, but that are not working together for a common goal or problem solving together, they are playing independently of the other children.
Now even if your child does exhibit cooperative play with other kids, not all the other children in a two year old class will (the majority will not).
2. By age three children in a preschool program will be potty trained, this eliminates the need for teachers to devote a great deal of time diapering and/or potty training, and/or cleaning up accidents, which gives them more time to plan activities and interact with the class. It also builds up your child independence and self reliance because they are encouraged to use the potty themselves.
3. Emotionally, by age three children are ready for the more structured environment of a preschool classroom. A good "Preschool" class, as opposed to a daycare classroom, has a fixed amount of time usually for threes 2-3hrs twice a week, in which the children participate in a variety of pre-planned activities that establish order and routine.
Prior to age three many children are not emotionally ready for the stress of entering a structured program, even though they love to play, or are outgoing, the repeated process of going to class can become difficult which is very bad for young children. Pre-school, is just that, a gentle experience in which children have experiences that lay the foundation for all of their future school experiences. If they are not emotionally ready, they develop a fear or anxiety toward school and possibly learning that can have life long repercussions. The reverse of that, is that when they are ready for school, and are enrolled in a program that meets their age and stage of development, encourages them without pushing and allows them play and explore in a safe and fun environment, they learn that school is fun, they build their confidence and develop a positive attitude regarding school they will help them for all of their school career.
So, my advice (long-winded as is is) is to wait. Three is perfect, usually. And one more thing, when you find a preschool you like trust your child. Give them three weeks to adjust and if they seem unhappy, ask to observe during class, if the kids aren't allowed free-play or given choices, or required to sit for more than 10 minutes at a time-RUN-that is a BAD program. And if they are not excited to go to school after three weeks, find another program or wait another 6 months. It is critical that their first experience is positive. For the few kids that have separation anxiety, but have fun in class it usually takes three weeks for them to warm up and realize that they are safe and having fun-longer than that, trust your instincts-if your teacher is working with you, and seems to care and really try to make your child feel welcome, and you know it is your child, not the program, stick it out and trust that your child will learn to love school. Otherwise, never worry about upsetting a teacher or director-they should care about your child enough to want what is best for them, not every program is right for every child.