I have taught many kids in this age group over the years. For many years, I would match up the correct aluminum arrow with the bow: 1516’s with a 15# bow, 1616's for a 25# bow, etc. Recently, I have started using PSE Razorback carbon arrows, in .1000 spine at 28”. These are certainly a lot zippier than the corresponding aluminum arrows, and work for a wide range of bows up to about 25#. While they are a little more expensive than aluminums, they are cheaper than the average carbon arrow. I buy mine from Lancaster.
FWIW, my experience is that kids in the 8-10 age group are much happier with 15# bows, and are able to control them well enough to learn good shooting habits. Kids over 10, and women of just about any age, are happy with 25# bows until and unless they begin to take it more seriously.