I'm totally confused about public transport in SF. Sorry for the short notice, but I need immediate answers since I'm flying out in hours.

I understand that, to take cable car & street car & everything, a day visitor's option is to either pay with exact-change cash or use Clipper card. No credit card!

Even though I live in US, I don't ever use cash and in fact I literally have no US currency on me right now. I could withdraw $ at an ATM, but then everything will come out in $20's. But then streetcar is like $2.75 / $1.25, cablecar is $7. Omg do they seriously not take credit card?!! If I walk into any bank in America, will they break a large bill into small ones / change (even though I'm not their customer) or do they frown upon such request?

And if I get this Clipper card, the info on this is very vague/inadequate. So there is an Info Booth on arrival level of T3 at SFO where I can buy this for $3 (doesn't say anywhere about whether/not Youth version of Clipper card is available... just says you can preorder them online, but obviously there's no time for that now). Is it possible to get this Clipper Card, both adult and child versions, at SFO with values added, AND pay for it all using credit card? Or can you only get the card there and then you have to figure out other ways to add values to this thing?