When do I transplant my cucumber seedlings?

Well I have actually already transplanted the seeings b/c they were getting really tall??? but now that I have them tp, some of them r starting to wilt just at the stem above the soil. R they to heavy, and Do I need to get lattice already for them to grow on? they don't have "true leaves" I guess to even start growing vine-like yet??? I just don't want all of them to do this! Please help :'(