Downplayed: The cast are shown playing with toy versions of their weapon in a flashback.
Justified: The familiar action of pulling back something elastic meant Bob took to archery as he got older. The same goes for the rest of the cast (Alice loved to burn things and went straight for the fire spells, Claire continued to feel comfortable carrying a staff after becoming a healer, Danny simply transferred his chopping skills to war axes and Elaina continued down the slippery slope until she jumped off it).
As a child Bob is shown practicing with a wooden sword and making fun of his Aloof Older Brother for training with a bow.
As a child, Bob is training with a bow while his Aloof Older Brother tries to save the world armed with a slingshot.
Subverted: Bob appears to be playing with a slingshot... but immediately hands it back to Black Mage Alice.
Double Subverted: ...who proceeds to use it to launch burning bits of paper.
Parodied: The protagonist's parents are shown using the same weapons as them (which include slingshots, BB guns and wooden swords) and doing their best to ensure they follow in their footsteps.
Zig Zagged: Some of the characters played with meaningful toys as kids, some didn't.
Averted: No one is ever shown as a child.
Enforced: The child versions are shown with the weapons to maintain the same iconic character silhouettes (but in Super-Deformed form).
Lampshaded: "Let me guess Bob, you're the kid with a slingshot and the woman with the bow's your mum?"
Exploited: Bob et al's parents wanted their kids to be adventurers. So they gave them their toys/weapons/chore to make sure that they'd pick a weapon they knew would allow them to form an effective group with.
Defied: "No, the lady with the bow's Claire's mum. She forbade her from using it so she wouldn't grow up with broad shoulders."
Discussed: "Which kid belongs to Bob? Just find the one with the slingshot."
Conversed: "Ah, a kid with a slingshot. I bet it's Bob."
Deconstructed: All the characters had disturbing childhoods, hence why their childhood interests eventually turned to combat.
Reconstructed: ...but only because they decided they wanted to be adventurers when they grew up; a highly respectable profession in their universe.
Played for Laughs: Bob gives his kid a slingshot hoping he'll follow in his footsteps.
Played for Drama: The cast are Tykebombs. Even their playtime was just another form of training...
Here's a beginner's link back to Weapon Jr. Aaaaww... They grow up so fast.