Perhaps, but frankly, nothing guarantees it's "to help them clean". Sure, it's the most probable situation, but it still can be "Okay kids, we allow you to go to your uncle and help him clean his attic".
When we use the verb allow, we implicitly give permission, but don't say it explicitly.
For other verbs where something intangible (like permission) is granted, or given (etc) to the subject, is the subject generally declined in the dative in Polish?
I'm afraid that it may not work outside of Irish English, and well, a lot of people learn English here - if they wrote that on a test, they'd rather be failed :|