Their height is typically determined by light intensity. So in other words, stronger light = shorter sprouts. This doesn't factor in light quality. As an example, I know my sprouts under full LED barely reach 1/4 inch before they start to show leaves. My sprouts under T12 get up to 1 inch if the light isn't directly above. If you have tall sprouts, get the light closer, or add stronger light. As far as average is concerned, I'd say under 1 inch and your golden.
Do you use a ufo on your seedlings? 90 watt ufo has 2 1/4" seedlings, it was really far up now it's about 8 inches above them. Any closer and the footprint is too small. They will probably get taller, although have some room inside the pots to cover about 1 1/2 inches of the stem. They have the cotyledon leaves and seedling leaves, just not the true leaves yet, they are 2 days from breaking soil. Starting them in the bigger pots may not have been the best idea due to footprint.
Last grow I used two glowpanel 45's on 8 seedlings, all of them stayed really short. Stretching always seems to be the result of lighting. Maybe you could add in some CFL just until they get some leaves going on.