The size they are in now looks fine. (for now) Tisn't a catastrophe using those pots...just a pain.
I start in a 2-cup pot, then 1 gallon, 3 gallon, and finally to a 5 gallon pot which takes me thru harvest. (all of 'em are plastic)

Water them so all zones of the soil gets moist when you water. Add half the water you intend on giving, then a few minutes later add the rest. This allows soil to absorb the water rather than it finding a quick path out the bottom. Then let the soil dry till next watering.
In a couple of weeks, start the nutes. (half-strength, observe the results) Eventually, (likely a couple of weeks) you'll work up to a full-strength mix once they acclimate.

So how are your youngsters looking now?
Rusty Trichome Reviewed by Rusty Trichome on . 10 Days old, Northern Lights (Sensi), FFOFS, Poss PH? My friend is a med patient and let me take a pic of her plants because she is worried. I told her I think it's PH but who knows. The first pic had 4 leaves when it came from the seed and has new growth coming from below the first set of leaves and above. Pretty strange. But it appears to be in the worst shape out of them all. Only a few are having this problem. She sprayed them with Safe-Soap. The first week the seedlings grew around 58ºF-65ºF. Now they are steady between 72ºF and 82ºF Rating: 5