Will our future children's thumbs be much larger because we are texting so much right now?

A vote in favour of Richard B's answer. Evolutionary adaptations occur when they increase an organism's life chances. The organism with a successful mutation will have more offspring and the adaptation becomes more widespread.

We don't acquire evolutionary features because they are cool or useful. Adaptations only emerge if they allow the organism to spread it's DNA more widely.

Texting is a transient technology which in 500 years will probably be a comic relic of the 21st Century "remember when people had to type messages on those little keypads they carried around, hahaha?". Texting probably won't affect our reproductive chances for long enough, or deeply enough, enough for it to have an evolutionary impact.

NO that is an old but mistaken ida of evolution

use of the body part does NOT cause the change

physical changes that by chance are more useful in a specific environment are favored.

texting may be ANTI-Evolution since those who text the most have sext the least

Probably fatter knuckles.

No, too many different sized keyboards.

that's not how evolution works.