Help with replacement tire and tube for little girls bike
For a four-year old, who will be riding around your backyard or at the park, any tire that holds air will be fine.  There's no MTB-specific tyres that small. 

Those tires will be totally fine on pavement and will work well enough on dry grass too.

The tyre specs in your link are for an 18" tyre (that's the measurement across the whole wheel) which is 1.95" in width, which is the horizontal width of the tread approximately.


  18" is unusual - is it possible that it reads  16" ?


Most tires have a ETRTO code - I suspect your current tyres will say something like 47-305 on the sidewall (or possibly 305-47 which is the same thing just reversed.) It means 47mm wide tyre, and 305mm across.

The bigger number has to match your replacement tyre, but the width has some leeway.

Could you please check your old tyres for the ETRTO code, and once you have that,  the replacement must match.   Your Amazon link doesn't show a ETRTO code sadly, but there will be many others that do.



Your other option is to simply inflate the existing tyres and see if they hold air.  Depends if they're just faded, or rotted to useless.   If there are bits of rubber falling off, they're definitely in need of replacement.



As for inner tubes, the ones on your bike now may be okay even if the tyres are rotted.  You will need to add some air and see if they hold overnight.

If you do choose to buy tubes as well, there are similar numbers to match in terms of size, but the tolerances are larger.

You'll need to get two tubes of course, but the box will cover a larger range of possible sizes.  See the front of this one which covers 340,349 and 355 sizes with the same tube.



Lastly you need to have the same type of valve as the old tubes - its 99% likely you will need a Schrader valve, same as on a car tyre.