if they have been vegging for 2 months and are still pretty small u might have another issue, what size pots are they in? post some pics if you can. i know my last grow my plants stayed really small because i allowed them to get rootbound.
as far as flowering they will go when thier photo period for flowering begins, they need a certain amount of darkness to trigger hormones that put them into flower. if you want them to flower sooner then you can put bring them inside after 12 hours of light, when u bring them in make sure you dont allow any light to hit them they need total darkness. can also build something like a box to put over them outside just make sure there are no light leaks