I don't know who told you these breeds were easy to sex the first week, but they are not. Sometimes barred rocks can be sexed by the quality of their head spots, but this must be specifically bred for, and it usually isn't.
Hatcheries vent sex newborn chicks to tell gender of their chicks with something like 90% accuracy, but this needs to be done by professionals to avoid harming the chicks. It's not practical for home raisers and I believe accuracy deteriorates after that first day of life.
You can start guessing on gender at about 4 weeks, maybe. Things should be pretty clear by 6 to 8 weeks.
The main thing to judge by at all of these stages is the comb. Size and color. Bigger, redder combs will usually be males. Smaller, paler combs will usually be females. Wattle growth is another good thing to judge by. Females usually won't have wattle growth or color before 12 weeks or so. Males usually will.
Post updates if you want help going forward and good luck!