Do I need a gaming computer to play fortnite and roblox?

COPPA issues notwithstanding (I'm assuming you've already taken care of the paperwork to allow your daughter to be on those sites / games), you can generally get by with a mid-range system for gaming...  HOWEVER, if you're wanting to record / stream their gameplay, the system requirements go up as the processor (& graphics card) have to pull double-duty.

For Gaming ONLY, the recommended requirements are:

* Processor: Intel Core i5-7300U (or better) / most AMD Ryzen processors

* Video Card: Nvidia GTX 960 / 1050 (or better) / AMD Radeon RX 560 (or better)

* RAM: 8 GB's (or more)

* Storage: 1 TB (or more, SSD ideal)

For Gaming AND RECORDING, the recommended requirements are:

* Processor: Intel Core i7-7700HQ (or better) / AMD Ryzen 5 (or better) processors

* Video Card: Nvidia GTX 1050 (or better) / AMD Radeon RX 560 (or better)

* RAM: 12 GB's (or more)

* Storage: 1TB (or more, SSD ideal)

Please be aware that these requirements are looking at more modern components that can be found with relative ease & using the game with the highest requirements (in your case, it's Fortnite).  As for storage, this is just a guideline & NOT a hard recommendation, mostly because you can add more storage with USB external storage drives.  You can get a portable 1 TB HDD for ~$50 (~$100 for a SSD) & a portable 4 TB HDD will go for ~$120.  Anything larger than 4 TB are non-portable (as they have their own power supply).

For recording / broadcasting, you'll note that the processor & RAM requirements are higher because the software you're using (OBS, XSplit, ect.) will need more processing power (at least utilizing some of the cores) & more RAM in order to crunch the video frames for your recording / broadcast.  If you choose to utilize your graphics card to do the video processing (on top of the game) instead of processor, you'll want to go up one generation (Nvidia GTX 1550 or AMD equivalence...  or better).

I will note that all three games are available on mobile devices, but the mobile device requirements are considerably higher, so you will need a high-end device (like Samsung Galaxy S10 or newer for phones...  Samsung Galaxy S6 Tab for tablets) to get Fortnite to run (which has the highest requirements... plus manual installation since it's not available in the Apple nor Google App stores due to current legal issues in the courts).

Gaming is mostly based on graphics processor. Among Us and Roblox can play on just about any modern Windows computer, but Fortnite takes a stronger processor to play well in graphics and smooth flow.

Although I can tell you minimum and recommended, unless you understood equivalent it's just speaking a language you don't understand. "Basic" has no meaning in a computer. There are very low performance cheap.

Since Yahoo Answers is global, it would help to provide much more important specific information in the question, rather than relative thoughts.

Location for shopping (we don't need an address, but a country and maybe city might help). Amount of money you have in mind. Are you referring to a new desktop PC or doing something with your current one? Provide what you have now by brand and specific model number if possible. 

The issue is not in download and install. It's generally with how well a game will run.

Anything online will run better as directly cabled to internet rather than wireless, and having a Solid State storage drive instead of an old spinning disk hard drive. 

Sure, $580 plus tax on a new gaming tower PC would be great.

https://www.bestbuy.com/site/ibuypower-gaming-desk...

That runs Fortnite at "Epic" (Ultra) settings on a 1920x1080 display at an average of about 60 frames per second which is maximum inexpensive monitors and TVs can run.

Although out of stock, I think it's more than you want to spend anyway. 

It does have a $170 CPU, $160 graphics card, $70 motherboard, $60 computer case, $80 in SSD and HDD, $30 in RAM, power supply, keyboard, mouse, wifi stick or card, is all put together with Windows 10 so is certainly worth the money it costs now, but back to what you have in mind?

A basic new tower style PC starts new at $300 or so.

$500 on sale is still good:

https://www.bestbuy.com/site/cyberpowerpc-gamer-ma...