these are just some tips.

In the future avoid peat pots.. they tend to dry out too quickly, or cause mold if too wet and can cause roots to stick too them making transplanting difficult.

if they're spindly, that is a sign of insufficient lighting. try to get the lights closer or get stronger T5 florescents, but be weary of heat so monitor the temperature above the canopy and use a fan with a slight breeze to circulate air if necessary.

depending on your seed starting mixture, they might need nutrients. typically seed starting mixes have little to no food. feed with some water soluble at 1/4-1/3 strength.

do not use heat mats, use them only when sprouting seeds and remove them as soon as the seed breaks the surface.

do not take them outside and back inside, constantly yoyo-ing them between sunlight and artificial light. does more harm than good. put them outside when they're ready to go outside and only bring them inside at night if the temperature dips too much. leafy greens are generally tolerate cold temperatures very well (ie kale survives 32F no problem)..

do not over-attend the plants. often time too much fiddling with them will do more harm than good. no need for egg shells or anything like that.

Good luck.

Don't know where you are located but if your nite time temps don't drop below 30F then young kale, collard, & mustard greens could take it ok. If that's the case I'd skip the indoor seeding and just plant the seed directly outside. I've been eating collards all winter (a rarity) since the coldest it's been at nite here was 20F, no problem, still harvesting them now due to the mild winter.

only reason for Osteried egg shells or DE cause of slugs and snails that are prob eating them outside in the hoop house