I have kids the same age and also run a homedaycare and have included some Montessori ideas. I have chose not to get a swing set because you have to also remember to put a certain amount of sand under it or mulch or rubber padding for licensing which adds to the cost. We have small slides, rocking riders for one and for 4 kids, play house, tee ball, badminton, jumpropes, large exercise ball, hula hoops, small sand box, bikes of all sizes, outdoor art easel, magnifying glasses for bugs, periscope for spying, variety of balls. We try to take a trip to a park regularly for more major climbing and swinging.
I guess that wasn't much help but best wishes for you in your search of a swing set. I would be interested in how you do montessori in your home daycare if you found some time to share what you do. I love hearing how other people are making it work for them.