So fair warning, I've never killed a mallard. But it's a goal of mine this year and I've spent a lot of time reading, buying, and blowing.
I have a haydel dr 85 and a duck commander triple threat. Both are pretty easy to blow and hard to screw up. The triple threat is IMPOSSIBLE to make squeal and it blows even if sopping wet. It is kinda loud and nasally though. The haydel is quite, not as raspy, but sounds ducky to me. I'd recommend either/both since they're both under 20 bucks.
Also, I suck at quaking. I got better after buying the art of commanding ducks and watching some of the early duckmen videos. I can't stand the later, reality TV stuff, but Phil and jase can call ducks. Their wood duck call makes the hair stand up on my neck. That was actually my first call, because we have billions of wood ducks down here.
You mentioned your son. For kids and folks like me who ain't the best at the quackin (we're quacker-lackin') a wood duck drake call or a 6 in 1 whistle is good. I have spent some time really paying attention to the ducks that live at the ramp by my house and that drake buzz is probably half of their chatter, the rest being little quacks and feeding sounds.
I'm carrying a triple threat, a gadwall call (that's 40% of our state harvest here, compared to less than a 2% average on mallards) a wood duck call, and a whistle this year. That lets me call pretty much everything I can expect to see. Mostly woodies and gadwal.
I have a mojo, but hardly use it. I really favor a jerk rig because you can go from barely making ripples to making waves. Fits in a coat pocket. I make mine a bit different from most folks. Happy to post it up if you're interested.