The funny thing about the bow, especially a medieval war bow, is that it takes a very long time to master. We’re talking years, here. It’s also heavily dependent on upper body strength, particularly in the back, arms, and shoulders. You need a heavier bow to deal with heavily armored targets which requires more strength and more practice drawing.
Here’s Matt Easton’s rant.
Basically, perceptions about the D&D Ranger along with Film/TV have caused a problem when looking at the body types or strength quota associated with archery. In particular, medieval war archery. The hunting bow and the war bow are different. While someone certainly could kill another human with the hunting bow, the draw weight is such that it will have a much more difficult time penetrating armor. This includes the padded armor made from cloth. War bows have a draw weight of around 60-70 pounds. The famous English or Welsh longbow was notorious for it’s difficulty and weighed in somewhere around 100-180 pounds.
Besides that, bows (and all weapons) require a great deal of care. You can’t just hide a wooden bow unprotected in a log for six weeks, come back and expect it to be useable. It must be oiled regularly to maintain it’s flexibility. It must be unstrung between engagements and restrung before the next one, thus requiring a fair amount preparation time. The must also be carefully wrapped when traveling to protect it from the elements. This is before we get into the required type of arrows, (heavier with a heavier head), and the difficulty in acquiring them. Which, if your characters are schoolgirls, may have a problem convincing the local fletcher on why they need bodkins rather than broadheads.
Regardless of how they get presented in fiction, the bow is not any easier to master than a sword. Your characters are better off with crossbows. However, it should be noted that the crossbows fire much more slowly and take more time between shots. They can be learned quickly, within a few months, rather than the years. They’ll still need to learn how to care for it and shoot it though.
Taekwondo black belts come in a few flavors which heavily depends on the system employed by their school and who trained them. Given how young they are, I’d peg them at starting their training between 5 and 8 with their black belt testing between 12 and 14. The average recreational martial arts student takes about 4-5 years to reach their first black belt rank. Sometimes you get the outlier earlies between 8 and 10, but a lot of programs institute a specialty curriculum for the really littles. (Our school had a special class for “Little Turtles”, which were for kids between 4-6 that had their own belt ranks and camouflage belts with colored stripes to denote their rank in the system before they were introduced into the regular white belt class. I think it ran white to red.)
If they tested at 12 then they were probably preparing for their second degree test at 15, if they tested at thirteen then they were moving up on training crunch time, and if they tested at 14 then they’re still about a year off their second degree test.
Worth remembering that recreational martial arts are still recreational. They offer up some good skills and are helpful for self-defense, but they’re not on par with trained professionals and they’re still going to need to adjust to the psychological effects of combat. I’d give at least one of them the rudest awakening. You can probably get away with giving them the quarterstaff because they should’ve had some training on the bo staff. The two aren’t comparable, they’ll be used to training on the rattan staff. Quarterstaves are actually heavier, thicker, and made of oak rather than bamboo. They are very solid and can do a great deal of damage. The range will also lend an advantage over enemies wielding swords.
I’d think about daggers, crossbows, cudgels, quarterstaves, and other varieties of low end but easily acquired equipment that don’t take as much time to learn. If you’re willing to have them take the time to learn and depending on the time period/country/rules at play, then it’s possible one might find someone willing to teach them the sword and buckler. It wouldn’t be a weapon with a shorter hilt that was primarily wielded one handed like an arming sword rather than the longsword.
I’d go through Matt Easton’s Youtube Channel for ideas.
Wiketenaur is a library of European 0martial/weapon treatises collected by HEMA. It’s helpful if you know what you’re looking for and are willing to slog through Medieval and Renaissance language.
You can also check out Skallagrim’s page.