There are different signs that can indicate whether a chick is male or female. Often it is easier for me to say that it is a boy than to be sure if it is a boy or girl. On extremely rare occasions I can tell that one is a boy a day or two after hatch. I can typically tell the sex of mine at 5 weeks but I remember one that I thought was a girl until he was 15 weeks old. These things are often just signs that they might be. I think it is often more art than science.
A male "tends to" develop his comb and especially wattles at an earlier age. They are not only bigger, they are often dark red compared to yellow for the girls. To me this is easier if they are single combed, pea and rose combed chicks can be harder. Notice I said "tend to" not that they definitely do. I've seen a lot of yellow combs on boys.
Males "tend to" have longer and thicker legs than the girls. Of course breed can affect how legs look so it is even harder to use this with mixed breeds. There can be variations within the same breed too. Still, I use this a lot.
A cockerel "tends to" have more upright posture than a pullet. Pullets tend to bend over more. Body conformation can give some hints too.
Cockerels "tend to" be bolder and more curious than the pullets. Cockerels are more likely to come to the front and greet you while the girls hang in the background. This can be a trap if you are selecting which chicks you want. The boys have more personality so you fall in love with them.
After they have molted in adolescence the feathers can give a clue. The boys' saddle and hackle feathers are pointed while the girls are rounded. They could possibly be a different color or shade also, depending on genetics. This is often after 12 weeks of age.
Yours are a little young but I'll offer some guesses. I think both are probably boys based on thick legs and upright posture. I do not see any wattles or red combs. Do not do anything drastic or dramatic based on my guesses. They are still too young.