Desperate to clear the drain in the tub (after weeks and weeks of struggles), I was told to try a sulfuric acid drain cleaner. Very carefully, I tried it... and now it's SITTING in the tub. NOT draining. Please tell me there's something I could possibly do myself. I have NO money for a plumber. None. Any safe advice is appreciated.
~~Stupid, desperate single mom :(

First you need to ventilate the room and keep the kids out. Very carefully scoop out as much water as you can into a larger container and pour it into a working drain and rinse well. Real plumbers will be along with the next steps. You may need to add a neutralizer before you can add anything else. I think lye crystals are still the best, first removing all standing water. It can take a while to work, so you walk away and wait.

A $2 hair trap would have prevented any of this. Small children might leave small toys in the tub and nothing but disassembling it will get it out.

Answer back what you think the age of your bathroom plumbing is.

This house was built in '49 or '50. Some plumbing was updated, like the trap under the tub, and a few feet of pipe is now PVC, but come is old original pipes...

Also... can the "working drain" be the toilet nearby? Otherwise I have to get it to the kitchen to have a working drain. The bathroom sink is also holding water. :(

Any working drain. If you can get to the plumbing in the cellar, look for a cleanout plug, under a trap or off to one side, in the PVC. Use an adjustable wrench, stand back, and have a bucket. If none, the next step is to snake (maybe $10) from the drains above. If snaking doesn't work, you cut into the PVC with a hacksaw and have pieces on hand to glue back on. You need a can of cleaner and a can of glue.

If you call a plumber and say that you have easy access to all the plumbing below the bathroom, it shouldn't cost too much. You might be able to hire a kid away from a hardware store. Draw a picture of the drains below and measure the diameter of the pipes and which is PVC or iron or copper or what.

So... I need to neutralize the acid with lye crystals before snaking or getting into the trap below the tub? Can this be found in a hardware store?

No, you may need to find a neutralizing product BEFORE you use lye or anything except water! Ask at a hardware store or call a plumber and ask.

DO NOT ADD ANYTHING TO NEUTRALIZE! An exothermic reaction could result, lots of heat, and is dangerous. Unless we are absolutely sure that what you have IS sulfuric acid it would be difficult to advise what to do. If you choose to bail the acid out, be sue to ventilate the room, wear protective gloves, face shield, etc. Just by accidentally rubbing a drop into your eyes could cause a lot of regrets.
Calling a local poison control center may help. Get the bottle for information and ask what they advise to neutralize the cleaner. Be clear to them that it is in the tub, not in or on a person.
Over the counter drain cleaners are dangerous and must be handled safely. Even snaking the drain after treatment carries the risk of residual acid getting on skin or in eyes.