Help with sentence and correction in D'Ooge Section 276

The sentences aren’t numbered in the first part of this section, but it’s the antepenult sentence of part one.

Aestate filii agricolae perpetuis laboribus exercentur nec grave agri opus est iis molestum.

First of all, I would like some help with the first clause but I would also like to make a correction. The answer key reads as follows:

In the summer the sons of the farmer practice with continuous labour

But exercentur is a passive verb, so shouldn’t it be:

In the summer the farmer’s sons are exercised

Now I need help with perpetuis laboribus. If it’s in the plural shouldn’t it be: continuous labors.

And the correction I would like to make in the second clause is as follows; the answer key reads:

And the heavy work of the fiels is not troublesome to them.

Wouldn’t a better translation be:

And the hard work of the farm is not troublesome to them.

Agri can also mean farm, not just field, and perhaps couldn’t be translated as fields since it’s in the singular.

So shouldn’t the complete correction of the sentence should be:

In the summer, the farmer’s sons are exercised by continuous labors nor is the hard work of the farm troublesome to them.

I would like some feedback on perpetuis laboribus though.

And I almost forgot: section 276 is found in page 23 of the answer key and in page 122 of the workbook.

Or perhaps instead of exercised, trained could be used?

In the summer the farmer’s sons employ themselves in unending toils and the heavy work of the field is not troublesome to them.

I created a Google document out of the pdf. That will make editing easier, although the formatting is now slightly different.
Thank you. Keep up the good work!

I’m wondering how it could be, employ themselves. As I mentioned, exercentur is passive. So wouldn’t the following make more sense:

In the summer, the farmer’s sons are employed in unending toils and the hard (or heavy) work of the farm (or field) is not bothersome to them.

And could someone tell me in what ablative use perpetuis laboribus is in. I would much appreciate it.

Thank you.

See https://logeion.uchicago.edu/exerceo II A β

With se, or pass. in mid. force; and in part. praes. and gerund., to exercise or train one’s self, to practise: si ad hoc unum est natus aut in hoc solo se exercuit, etc., Cic. Or. 28, 99: se vehementissime in his subitis dictionibus, id. de Or. 1, 33, 152: se in consultationibus, id. Att. 9, 4, 3: sese ad cursuram, Plaut. Most. 4, 1, 5: se ad velitationem, id. Rud. 2, 6, 41: sese quotidianis commentationibus, Cic. Brut. 71, 249: se genere pugnae, Caes. B. G. 1, 48, 4: se genere venationis, id. ib. 6, 28, 3: se saliendo, Plaut. Bacch. 3, 3, 25: cur non in utrumque protinus locum se exerceant? Quint. 4, 2, 29 Zumpt N. cr.: Jovem Olympium, eum ipsum, cui se exercebit, implorabit, Cic. Tusc. 2, 17, 40: cum athletas se exercentes in curriculo videret, id. de Sen. 9, 27; so, ad virtutem, Vulg. 1 Tim. 4, 7.— Mid.: ut exerceamur in venando, Cic. N. D. 2, 64, 161: ut in utrumque locum simul exerceamur, Quint. 5, 13, 50: faciunt idem, cum exercentur, athletae, Cic. Tusc. 2, 23, 56: Ciceronis pueri amant inter se, discunt, exercentur, id. Att. 6, 1, 12: ne aliter exerceri velint, Quint. 3, 8, 70: in mandatis tuis exercebor, Vulg. Psa. 118, 15.—Act. part. in mid. force: cum, ceteris in campo exercentibus, in herba ipse recubuisset, Cic. de Or. 2, 71, 287; so, ipsique dictata exercentibus darent, Suet. Caes. 26: spectavit assidue et exercentes ephebos, id. Aug. 98; cf.: si ludicra exercendi aut venandi consuetudine adamare solemus, of exercising ourselves, Cic. Fin. 1, 20, 69, v. Madv. ad h. l.—