でもｖｓ。だっても

[Shiroisan]

子供でも分かるでしょう。
子供だっても分かるでしょう。
大人だっても分からない

This is old grammar I learned a while ago, but I've recently heard both of these used and I suddenly got confused on what the difference is, or if there is even a difference, or perhaps if one is simply incorrect?

Help is appreciated

[Ongakuka]

As far as I can tell, だっても has the same meaning as　だって (on its own) but the latter is far more common, I think.

一日だっても休んだことはありません
一日だって休んだことはありません

I guess adding も increases the emphasis on 'not even one.' As you demonstrated in your examples, でも has the same meaning and is usually interchangeable with だって（も）, however the latter (especially without も) can sound a bit casual, like spoken language, whereas でも is more 'proper' I guess.

Also だって has a special usage for making excuses or explanations:

だって、傘を持ってきてって言われたから

I'll assume you're already familiar with this usage

[Shiroisan]

thank you very much .

It's good to hear that there's almost no difference in that context. As for the other useages of だって I think I'm alright with them.