If you want a no hassle gun I'd suggest a standard power Gamo or Crosman. Normally I'd say Crosman, but Gamo are usually a pound lighter for kids. They're usually ~28lbs to cock, but vary +-2 or so lbs.
What I would do, but it requires a bit of work, is I'd take the same generic gamo (a standard $100 model claiming 1200/1000fps), then take out the spring spacer which reduces velocity ~250-300fps and cuts cocking effort in half or more. My Crosman with this mod cocks at 12lbs! It also tames the gun drastically, smoother, quieter, more accurate etc. You can also adjust the power with a custom length spacer of pipe, or washers to adj power up as he grows. The mod is easy, aside from removing the spacer it needs a little piece of plastic or sheet metal added that you can make. I can explain if interested in doing all that.
Another option is a Crosman/Benjamin Titan with the low power nitro spring. Normal weight gun but probably the easiest to cock. They don't drop power too much, maybe 50-100fps, but cocking effort drops from ~30 to ~22. They're often on sale for $100. The problem is I've only seen them in .22 so if you need a 177 then a barrel is $20 delivered. That's the gun I'd want if I were a kid... It weighs about 7lbs, plus another 12 or so oz for the scope which is required and comes with it, however the replacement barrel can have open sights if you want.
Stoeger makes an X5 and X3 kiddie guns which you might look into, but I've never seen one so I can't say if they're worth having. I'd be very wary tho.