Donation in lieu of wedding favors

It's definitely not rude to forgo favors. Most guests won't even notice there aren't any. But there's also no reason to announce you are donating because it doesn't really have anything to do with your wedding. Just donate however much you can afford. If you are worried it's not enough, you can cut back on some other wedding things, too, in order to increase your donation (fewer flowers, less expensive attire, shorter photography time, etc.).

It’s not rude at all to forgo favors.

Yep, skip the favours that will only really end in the landfill anyway. The donation is a lovely idea, but as others have said, it's probably best to keep that private.

I think it's lovely that you want to donate to a children's charity and I guess if anyone does ask about favours you can just tell them you've donated instead . But it doesn't need to be a big announcement. People might not even realise that favours are missing.

Agree, I would never look for or want wedding favors but if someone had signs saying they donated my favor, that might make me feel wierd lol

You don't need favors at all, but it's super weird to do a donation to a charity (that someone may not support or care about for whatever reason) "in leiu" of something that already doesn't matter. Make a donation if you'd like, but just skip the signs about it and don't worry about other favors.

If you do really want favors, edible ones are the way to go. Cookies, truffles, etc that people can grab on the way out.