• Meta and Google are serious competitors.

• But they can also do business together: Turns out Meta's Instagram was buying ads, targeting teens, on Google's YouTube.

• There are questions about whether that campaign was legit. But as far as giving your rival money to help build your own business? That seems pretty standard.

Instagram is huge. But Mark Zuckerberg would like it to be bigger, and younger.

One solution: Pay one of his biggest rivals for help.

Meta's Instagram ran ad campaigns on Google's YouTube targeting kids earlier this year, the Financial Times reports. That is: Meta paid Google so it could reach Google's users in hopes of turning them into Meta users, too.

The FT's story focuses on whether Google, Meta, and an ad agency broke rules about advertising to kids. And we can discuss that in a second.

But to me, the striking thing is what the campaign says about both Instagram and YouTube: that Instagram, which used to be a service kids used because their parents were hanging out on Facebook, now worries it's a site for the olds. And that people who understand the internet understand how huge YouTube is with kids, even though adults remain profoundly unaware of just how big YouTube is.

This wouldn't be the first time someone has tried boosting a big internet property by harvesting users from a rival property. TikTok helped vault itself into world domination by spending at least $1 billion on ads on Instagram and Snap in 2019. More recently, Temu has become Meta's biggest advertiser and is spending big on every other property on the internet, too.

That kind of ad buying ought to pose a dilemma for all the sites selling space to their rivals. In the short term, they're getting paid. Long term, they're helping a competitor get more competitive.

But that doesn't seem like it's a real dilemma, after all: Given the choice between money today and a problem in the future, sellers take the cash up front.

As far as whether that ad buying is legit? That's up for debate.

Very quickly: YouTube has a policy that prohibits using age or any other demographic info to target anyone under 18. But it allows ad buyers to pick an "unknown" age option when they target ads. And the FT says that people at Meta, YouTube, and a third-party ad agency all believed that using that age bracket meant they'd really be targeting teens.

Meta says it didn't do anything wrong. "We've been open about marketing our apps to teens as a place for them to connect with friends, find community, and discover their interests," a statement from the company says. It also argues that using the "unknown" category is above board and available to any ad buyer.

Google, meanwhile, is a little less definitive.

On the one hand, the company says: "We prohibit ads being personalized to people under 18, period. These policies go well beyond what is required and are supported by technical safeguards. We've confirmed that these safeguards worked properly here." But on the other hand, it suggests that maybe someone, or more than one person, colored outside the lines: "We'll also be taking additional action to reinforce with sales representatives that they must not help advertisers or agencies run campaigns attempting to work around our policies."

So that option may not be available to future ad buyers. But if a rival wants to buy ads from YouTube some other way? That's probably 100% OK. For now.