If what you mean by “okay” is that you won’t “get in trouble” with Airbnb, making an exception to your children guidelines, especially after having a conversation about it in Airbnb messaging regarding all the warnings, caveats, etc. is “okay”, but make sure there aren’t any kind of grossly unsafe or negligent conditions.
In most places, I don’t believe you are allowed to refuse children in a full-house rental anyway, although I have seen that point argued here. Although this isn’t an official source, the person quoted below seems to have experience with this:
“Speaking from personal experience, hired legal counsel, and almost being banned from Airbnb.
If you live in the house also (renting out extra rooms while you reside there) you can discriminate and ban children from living there legally.
Actually doing this is not that easy, you can mark 'not suitable for children or infants' which will make your listing not show in the search results if somebody searches for houses after putting in this information. But if somebody finds your house and during booking puts in '2-adults and 3-children' they can still book (It is simply changing the search results to not include your home).
If you do not live in the house and it is a full home rental you absolutely CANNOT discriminate against families with children, it is protected federally, statewide, and on the county/city level under Familial Status, which is a protected class. (I got in trouble for trying this last year and hired an attorney).
If you live there you get more control, you legally can discriminate against pretty much whoever you want (Not saying it is the right thing to do, but legally you can). If full home rental you cannot discriminate against anyone. (United States, unsure for the rest of the world)”
I find that making exceptions in the right circumstances is helpful, because it gives me the opportunity to mention all of my warnings and concerns without being too inhospitable. In this case, something along the lines of: “Because you have been so thoughtful to ask me about this, for you I will make an exception. Just please make sure you watch the child at all times, keep little hands clean, and confine food eaten to the kitchen area”.
Also, to protect yourself against the antics of both children and adults, please make sure you get a short-term rental insurance policy with a sufficient amount of coverage, to supplement anything you might be able to get from AirCover, Host Guarantee, etc.