ORIGINAL: nickj
I would be upset. I don't know how lax they are at other fields, but at our field NO ONE is allowed anywhere near the runway except to retrieve a stopped plane, and only then after announcing loudly. We have a low catch-fence about 30 ft. from the runway, and everyone stands behind it. If you don't have a similar set-up at your field, then common sense should apply. IMO, common sense would dictate that you don't practice taxiing on the runway when planes are in the air. I disagree that what the father and son were doing was okay.
I don't think that taxi practice is an issue at all with a plane in the air. At my club, if you are not winged you cannot be out unless it is a training night, so this father / son thing would have been off side.
Other than that I have no real problems with what they did, you called out a landing, they gave you the runway, was not perfect, but they did what they should do overall.