ALL baby cockatiels have the markings of a female (if the color morph permits). So, this baby is a pearl... at the moment this is female patterns. When he/she hits around 6 months or so of age he/she will go through the first molt, molting out all the baby feathers and growing in the more adult feathering. If it is female, the feathers will come back nearly the same as in the picture... if it's male on the other hand... it will be solid in color, and will lose the white/yellow beading in the feathers... but he will still be a pearl. Only way to know 100% at this age if it's male or female is with DNA sexing.
Just to add on, i noticed from the photos that you are using wood shavings as bedding. I would reccomend that you would use newspaper or other paper as bedding, as woodshavings/corn husk have been known to cause respatory problems for birds. Especially your young baby might be extra sensetive to this.
That bedding is fine to use! But it makes one heck of a mess once they start flopping. But this baby is rather young and should still be on formula.
Like it was mentioned above, once the first major molt comes you'll know if a male or female. As females retain the pearl coloring while the males turn to regular grey. If the breeder knows the parent's genes, it would be easier to determine the gender of the offspring.
If the mother didn't look the same as this chick, you have a hen.
I see one, if not possibly two, sex-linked mutations in this chick.
Without knowing the mothers mutation, everyone has a 50/50 chance of being right! And, as mentioned, you'll know once this chick starts molting in adult feathers!