I own about 20 air guns. In the price range you specify, I personally like the RWS 94, 93, 34, and 24. My 94 clocks an honest 934 f/s (avg) with 7.9 CPLs (cost around 160 bucks if you can find one) and I think one of the best air gun values around. It is a clone of the famous FWB 124 and is very well made. The 93 is plain looking but is 'extremely" accurate (a sleeper) and can be had for around 120 bucks - clocks in the 740 f/s range. The 34 is a great gun IMHO - most folks seem to get in the mid to high 800's. The 24 is one of the most accurate guns around for the money (around 150 bucks) but generally shoots in the 535 f/s range so not the best for hunting - My 24 and my 93 are more accurate than my Beeman R-7, which cost more than twice as much. The RWS 24 is a smaller gun and could be the ticket for your younger son. I also have a Quest 1000 and find it less accurate than any of my RWS guns and a bit rough. The trigger is typical Chinese and needs to be replaced, which I plan to do. I have also owned a RM 600 (Mexican), TF 99, and TF 97 (99 and 97 are Chinese underleavers) and would not recommend these guns for a kid - I got rid of mine. They generally need work to make into good shooters and can be a bit crude. I have found the German and Spanish made RWS guns to be of superior quality and they also have a lifetime warranty.
Good luck,
Jim