How did he guess that would be the answer. 

"When's a good time for you? Central City's an hour behind Toronto..." 

Flash arranges a patrol for one evening when the boys are free.

They'll meet at the Central City zeta tube entrance, which is hidden in an abandoned construction site. "The destination code's 008. If I'm not there, wait a minute or two then go home or here instead. I don't want you going looking for me." 

"For a particular reason, or...?"

"I'm a speedster. If I'm more than a few minutes late, that's not just 'something came up'. It's 'something came up that I couldn't handle', which means I don't want you trying."

He looks straight at Impulse, trying for stern.

"This isn't about whether you can do it, or how much I trust you, or anything like that. But you're under 18, and that means..."

He pauses to get the wording right. "It means you're my responsibility during a patrol. If I've run into something I can't handle, you don't come help me, because that puts you in danger too. You get away, and you call the League so they can help. Okay?"

"If I think you're in serious trouble I'll call the League, and I'm not going to assume by default that it's a good idea for me to get involved on top of that - but if I have an actual reason to think it's worth it, taking the consequences into account, I will."

"I'm much more natively inclined to run away from anything that gives you that much trouble, but I trust my brother's tactical assessments," says Warp.

"I suppose I'll have to live with that," Flash says with a sigh.

He reaches up as if to run a hand through his hair, but ends up scratching the back of his cowl instead. 

"It's not likely to happen, anyway. I'll meet you at the zeta-tube, we'll go on patrol, maybe we'll stop a few muggings or a bank robbery. Nothing too exciting." 

"Yeah," says Impulse. "Oh, by the way, Mom wants to meet you, want to come by for dinner after patrol?"

Flash thinks about it before replying. He doesn't have anything scheduled - never does, after a patrol - and it would be responsible to meet his sidekicks' legal guardian at least once. 

"As Flash or in my civilian identity?" he asks, grinning. "Do I need to bring a clean shirt?"

"Up to you whether you want her knowing we rhyme, I guess!"

He laughs.

"Sure, why not. We'll see if she finds it as amusing as you do." Probably not - Impulse seems to do most things more intensely than other people. But maybe his mother is where he got it from. That could be interesting. 

Giggle.

When it's time to go on patrol, the zeta tube network spits the twins out into the concrete shell of a half-constructed building. 

Their mentor doesn't seem to be there waiting for them. 

Their mentor is bizarrely un-punctual for a speedster. There's no reason to worry until it's been a minute or two.

But they probably shouldn't stand around in costume waiting for him, so they might as well zip around the immediate area for a bit, and once they're doing that they might as well also take the opportunity to look for items of interest such as 'signs of obvious supervillain activity they should interfere in or tell the League about' or 'the Flash, zooming sheepishly toward them'.

Oh look here's a zooming speedster.

...he comes to a halt in front of them, looking sheepish.

"Sorry, sorry. Hope I didn't worry you." 

Impulse giggles.

"Don't worry," says Warp, "we pretty much expect it by now."

Flash laughs along. He's well aware of his lateness habit - it used to be worse before he got his superspeed. 

"Shall we get started?" 

Bounce. "Yes let's!"

Flash's patrol route is one which takes full advantage of his superspeed - zooming on the fastest safe route between one vantage point and another, covering the likeliest hotspots for trouble in the city.

And, speaking of "hotspots"...

A man dressed in what looks like asbestos is waving a flamethrower around in the middle of a reasonably crowded street, laughing in delight as his surroundings go up in flames. 

Impulse glances at the Flash, for once actively seeking his input on how to proceed.

Flash ramps up the speed and babbles out a quick explanation.

"This is Heat Wave, I've fought him before, the thing on his left arm's a fire suppressant but we should get local authorities here as well - " 

He sketches out a plan of action, sending Warp to zip around rescuing civilians while he and Impulse try to disarm Heat Wave. 

The boys follow this plan!

Impulse, looking delighted at the puzzle in front of him, manages to find the safety shutoff on Heat Wave's fuel-tank backpack and flip the switch without otherwise disturbing anything.

And then he zips around in front of the villain and slows down enough to say, "Hi! You look like you're having fun."

"...well. I was." He sounds somewhere between petulant and bemused, like a kid who's just had a favorite toy inexplicably stop working. 

"Yeah, sorry about that," he says cheerfully. "If you want to play with fire uninterrupted I recommend doing it somewhere else. Neat flamethrower, by the way, did you make it yourself? I've built a few but they didn't work nearly this well."