I NEED HELP

so i planted about 8 plants when they were about 2 1/2 weeks with only a few sets of leafs. i planted the other 8 when they were just small 3 day old sprouts. Since then the sprouts have doubled the size of the older plants who are obviously stunted.

I was wondering what the future might hold for the stunted ones. Only 6 of the older plants have not grown much. The other 2 are right alongside the size of the sprouts and just have more leaf sets.