The structure of a joke arrives before the content
A cartoon cow joke with no real punchline, set in the same serious wood type as a proper one, because timing is what a small child learns first.

WHY DID THE COW CROSS THE ROAD, set small, in cream wood type. Beneath it, filling the chest: BECAUSE BANANA, set much larger. No drawing, no punchline mark, nothing else printed.
The timing is exactly right and the content is nothing at all — and that gap is the whole joke.
What is actually funny about "because banana"?
The delivery, not the word.
A real joke needs its answer to connect back to the question; this one has the shape of that connection — the pause, the confident answer, the size increase for the punchline — with nothing underneath it. It's the same appetite that drives a question asked three hundred times — testing that a form works before caring what it produces. A child has worked out that a joke has a machine before working out what the machine is supposed to do, and running it empty is, reliably, still funny.
Why does serious wood type do more work than a cartoon would?
Because a cartoon cow would announce that the joke is for children, and the whole point is that it isn't trying to be.
Set the same way an actual proper joke would be set — the small setup line, the oversized punchline — the design takes "because banana" completely seriously, and the mismatch between that seriousness and the answer is what makes a stranger laugh at second glance rather than dismiss it as a kid's doodle on sight.
Is printing a child's non-joke just laughing at them?
No — the laugh lands on the shape of the joke, not on the child, and the two are different things even though they happen in the same second.
A child telling a joke that doesn't resolve is doing something genuinely impressive: performing comic timing correctly with content it hasn't learned to fill in yet. Printing it takes that performance seriously enough to set in type. Laughing at a child would be pointing out they got it wrong; this is closer to admiring the delivery of something that, technically, they got right.
Will they mind, later, that this got printed?
Some children are delighted to be shown their own early material; some would rather it stayed private.
There's no way to know in advance which one this particular joke-teller will grow into, so the honest approach is the one used for anything else of theirs that ends up on fabric — a drawing, a signature, an invented line of their own — decide for them now if a decision is needed, and ask once they're old enough to have their own opinion about it.
Does it work for a joke that actually landed?
Yes, and it needs almost nothing changed — the same small setup, the same oversized answer, just an answer that happens to make sense.
The design doesn't depend on the joke failing; it depends on the joke being delivered with total seriousness. A genuinely good line that actually resolves gets the same treatment and reads, if anything, more confidently, because there's no gap left for a reader to notice.
Does the wording have to be exact, or does any of their material work?
The exact wording is what makes it theirs — the same joke told by a different child, in different words, is a different design.
What carries over between children isn't the joke, it's the format: a small setup line and one outsized non-answer, set in type that refuses to wink at the reader. Somebody else's version of "because banana" would print just as cleanly; it just wouldn't be the one that happened at your table.
Does it print well?
Yes — wood type is already flat, hard-edged and built for a single ink, which is close to ideal for a garment.
Cream on tomato red holds the contrast without a gradient anywhere in it; keeping the setup line noticeably smaller than the punchline is what makes the size jump read at a glance rather than needing to be read twice.
How do I get one made?
Describe the joke at JustOG — the exact wording, which line is the setup and which is the punchline. Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to order and shipped.
Designs other people have published are in the shop.
Nobody has laughed at "because banana" in this house for years, and everybody still remembers it.