what causes small leaves?

I have 2 plants I mistakenly started off in jiffy peat pots and they look healthy except for the leaves are little mini leaves. attached are some pics of what i'm talking about, you can see in the one with the blue cups and jiffy pots the difference already. the cups are 3 days old and the jiffy pots are about 11 days old. why are they so small and how can i make them larger? how would i transfer out of the jiffy pot into a slightly larger container (maybe a cup) without damaging the sprout? thanks, d-oz.

P.S. - The pics don't really provide great detail in the difference of the leaf sizes, the older sprout's leaf sizes are about 1/3 size of the new ones but still look healthy and identical to the other ones, just smaller.

I have recently discovered a few things in my reading which may or may not apply since I can't back it up with studies. (However my understanding is they are going on.) Anyway, the jiffy is quite a bit smaller,young plants develop their root system first. If they don't have space to expand it's like a bonsai. Also apparently plants which are given initially a depth of at least 4" to send down the tap root have a significanly greater ratio of females to male. So I would cut off the bottom of the jiffypot and slice and peal off some side sections and pop what's left into a larger pot/cup, without disturbing the majority of the root ball. The jiffy pot will disintegrate in a couple of weeks, or you could try pealing off the JP and just transplanting. GL HH