At only 2 months old, it's nearly impossible to be able to tell the gender of Rosey Bourke Parakeets, and even as adults it's extremely difficult because the external differences are so very subtle. As adults, both males and females have a blue-colored line/band across their cere, but adult males tend to have a bit of a darker blue band, while the band on the females tends to be a lighter shade of blue or even fades away completely in some birds. The other exterior difference in adults is that the males have a very pale-salmon kind of color on their throats/necks. However, you cannot even begin to look at these characteristics until they are at the very least 6 months old, but even then it's usually too soon and you must wait until they are around a year old...and even then, these exterior characteristics are not usually pronounced enough in most birds to be counted-on for sexing them.
The only way to be able to identify the sex of Rosey Bourkes for certain (and even for a good guess) is by having a DNA-test done on them, either by blood from clipping a toenail or from an actual blood-draw from their neck vein, or by plucking a few fresh feathers from their chest. You can either have your Certified Avian Vet do the tests, or their are several places online where you can order a DNA test-kit, they'll send you the test-kit, you pluck a few fresh chest feathers from each bird, send them back, and in a week or two they'll mail you the results. The online tests usually cost between $20-$30 a bird, but if you're doing more than one bird a lot of places will do discount packages. At the CAV the cost varies based on the vet; some vets will not just do a DNA test, they make you pay for an entire office-visit or a "wellness-exam" in addition to paying for the DNA-test, though you should have all baby birds get a wellness-exam by a CAV anyway...But either way, that's really the only way to be able to sex a Rosey Bourke.
I wouldn't even attempt to guess what the sex of your babies are right now, they are way too young.