From what you given me, along with no pics, I have 2 possible problems. More than likely it is going to be the 1st one.

ok, your using miracle grow soil, right? You didnt mention what kind it is so I'll guess its the regular stuff. Sometimes it (the soil) will have too many nutes in it for young seedlings only a week old, such as yours. It will burn them right up. This could be your problem. It happened to me before, got some but not all.

Could just be a weak seed, that does happen where they just dont have it. They will just die for no apparent reason.

One thing, I wouldnt do is flush them. For one, the nutes are time release, so that just wouldn't work. And for two, you would just drown those poor things by flushing a week old seedling.

Your best bet, find some soil for seedlings. Something with little or no nutes in it. Then carefully, very carefully tranplant those bitches. If you wanna risk it and leave them in the MG, go ahead but I think if you wanna be 100% sure they pull through, transplant.

Peace