I offer my two cents as a mother of two, a former elementary teacher, and a current in-home daycare provider.
Unfortuntely, children are going to get sick often the first year (approximately) that they are exposed to a larger group of children. If a child is in a daycare when they are an infant, they will get sick often as an infant. If the child is home until being enrolled in preschool, they will get sick as a preschooler. If the child is kept home until Kindergarten, it will happen then.
Until they are exposed to the germs, they don't really build up many of the immunities they need. That first year exposed to a large group of children will expose them to the germs, make them sick, but also build up their immunities so (for the most part) they won't continue getting sick all of the time in the years following.
The only way to postpone the process is to limit the number of children they are exposed to early on. Look for a preschool with a smaller population or look for a home daycare with a preschool program.
I wish there was a way to avoid it all, but there really isn't. While I don't want my infant sick all of the time, I would prefer it happen during the preschool year than the elementary years. Just remember to wash hands all the time!
Good luck!