This chick is smaller than the other and has trouble pooping(the darkest one) he was born one day later and he is not that active what should I do he does not get picked on tho
Some grow faster than others so I wouldn't worry about that unless he's not eating. Not too sure about the struggling to poop, never heard or seen anything like that before. Maybe someone else might be able to add to that
Don't think you should worry at this point. I have a chick (the smallest of all it's brother's and sisters), she was also born a day or maybe even two after, has to help it out of the egg even, didn't move or do anything for about two days. We had to feed it with a toothpick and give it water with an eye dropper. We came to the conclusion that it was just premature.
Just give it time; see if it eats well, drinks water and like rosemary thyme said just check for pasty butt.
I also don't see a size difference because of the angle of the picture