Although at 8 years old, they won’t understand the complexity of the maths you use – you could explain how important it is and give an example.
Being a fossil, electronic calculators did not exist during my schooling – so everything had to be worked out longhand. Now I’ve become lazy and use a calculator for some very simple calculations, but very importantly, I know the approximate answer. Many a time, not looking at the calculator display while keying in the sum, the answer is nowhere near that expected. I then know that I must have made a mistake, or not fully depressed a key during the process.
As a real life example, back in the 90s I had a school leaver working with me – groups of 4 numerical values needed to be averaged (a very simple task for a calculator and very easy to mentally check that the calculated result was correct, since all the numerical values were around 65 (given to 3 decimal places)).
Using a calculator, the school leaver had written the calculated answers beneath each group of 4 numbers required to be averaged. All of the calculated results were around 65 (as expected), but one result was around 260 – the school leaver seemed oblivious to the fact that this may not have been correct.
So perhaps you could stress the importance of having the maths skills required to know that the result (given by the calculator/computer) is somewhere close to that expected.