First of all I was raised in Indiana on meat and taters. Eating out meant pizza or hamburger. Never tasted any Mexican food til I came to Texas.
The one thing I have never learned was how to eat a taco without everything falling out the bottom. &%$#@ dang food!!

Use both hands

One to hold the taco and one to hold the plate to catch part that falls out

Tacos are supposed to be soft.

Set the plate on a table like a normal person

It was a soft taco filled with sausage and cheddar. Folded over once. Remember your high school physics? For every action there is an equal and opposite reaction.
I bit down and half the filling hit the floor.

mmmmmmmmmmm tacos

My 4 year old has the same problem

Give her another 6 moths to a year and she'll have it under control.

Shouldn't you be eating something healthy

Fold the back end over. Hold gently and tilt your head and bite. Rarely ever have that problem, and only with the last bite of the exceptionally gooshy stuff like guisada gravy and sour cream and refried beans. Biggest thing is don't overfill your taco. (Yes, I'm fully aware how awful all of this is sounding, no comments needed from the peanut gallery, thank you very much.)

Never overfill a taco?

It is supposed to fall out. You let it fall into the plat to be mixed in with the beans and rice, and sopped up with an extra tortilla. That is generally the best part of the meal.

Other than soup and maybe pasta I think it's easier to eat everything in a tortilla