Illud is the neuter accusative singular form of ille/illa/illud (pron.): that; he, she, it; the former (here this pronoun anticipates the accusative-and-infinitive clause that follows). Potius (adv.): rather, instead. Cōgitābis is the second person singular future form of cōgitō, cōgitāre, cōgitāvī, cōgitātum (1): to think (about), consider, reflect (upon). (You will rather reflect on that. . .)
Nōn: not. Esse: to be. Īrāscendum is the gerundive of īrāscor, īrāscī, īrātus sum (3, deponent): to be or become angry (takes a dative object; the gerundive can only be neuter and impersonal because the verb is intransitive). Esse īrāscendum is the impersonal passive periphrastic: that you/one must (not) be angry. Errōribus is the dative plural form of error, errōris (3m): wandering; error, mistake, delusion. (. . . (namely) that one must not be angry at mistakes.)
Quis/quis/ quid (interrog. pron.): who? what? Enim (particle): for, indeed, in fact. Sī (conj.): if. Quid sī = what if? Quis /qua/quid (indef. pron.): anyone, anything; someone, something. Īrāscātur is the third person singular subjunctive form of īrāscor, īrāscī, īrātus sum (3, deponent): to be or become angry (subjunctive because it describes a potential). In (prep.): (with abl.) in, on; (with acc.) into. Tenebrīs is the ablative form of tenebrae, tenebrārum (1f, plural only): darkness. Parum (adv.): (too) little, not enough. Vestīgia is the accusative plural form of vestīgium, vestīgiī (2n): footstep, step. Certa is the neuter accusative plural form of certus/certa/certum (1/2): certain, settled, sure, unerring. Pōnentibus is the m/f/n (here m) dative plural form of pōnēns, pōnentis (3), the present active participle (placing, putting) of pōnō, pōnere, posuī, positum (3): to place, put, set up. (For what if someone were to be angry with those not placing sure enough footsteps in the dark?)
Quid, sī quis: what if someone (see above). Surdīs is the m/f/n (here m) dative plural form of surdus/surda/surdum (1/2): deaf. Imperia is the accusative plural form of imperium, imperiī (2n): power, authority; empire; order, command. Nōn: not. Exaudientibus is the m/f/n dative plural form of exaudiēns, exaudientis (3), the present active participle (hearing) of exaudiō, exaudīre, exaudīvī/exaudiī, exaudītum (4): to hear, listen (to); comply with. (What if someone (were to get angry) with the deaf not hearing orders?) Quid, sī: what if (see above). Puerīs is the dative plural form of puer, puerī (2m): boy; child. Quod (conj.): that; the fact that; in that; because. Neglēctō is the m/n ablative singular form of neglēctus/neglēcta/neglēctum (1/2), the perfect passive participle (ignored, neglected) of neglegō, neglegere, neglēxī, neglēctum (3): to ignore, neglect. Dispectū is the ablative singular form of dispectus, dispectūs (4m): consideration, regard. Officiōrum is the genitive plural form of officium, officiī (2n): duty, office (neglēctō dispectū officiōrum is an ablative absolute). (What if (someone were to be angry) with children because, consideration of duties having been neglected. . .)
Ad (prep.): to, toward (takes the accusative). Lūsūs is the accusative plural form of lūsus, lūsūs (4m): play, sport, game. Et (conj.): and. Ineptōs is the masculine accusative plural form of ineptus/inepta/ineptum (1/2): foolish, silly. Aequālium is the genitive plural form of aequālis, aequālis (3m/f): a person of the same age as another; a contemporary; an equal (a substantive use of aequālis/aequālis/aequāle (3): equal; of the same age; contemporary). Iocōs is the accusative plural form of iocus, iocī (2m): joke, jest. Spectent is the third person plural subjunctive form of spectō, spectāre, spectāvī, spectātum (1): to watch, look at; aim at; consider (subjunctive because it’s part of the potential situation that started being described at sī quis īrāscātur). (. . . they looked to the games and silly jokes of (their) equals in age?)
Quid, sī: what if (see above). Illīs is the m/f/n dative plural form of ille/illa/illud (pron.): that; he, she, it (those/them). Īrāscor, īrāscī, īrātus sum (3, deponent): to be or become angry. Velīs is the second person singular subjunctive form of volō, velle, voluī, — (irreg.): to want, wish; choose (subjunctive because it describes a potential situation). Quī is the masculine nominative plural form of quī/quae/quod (rel. pron.): who, which, that, what. Quod (conj.): that; that fact that; in that; because. Aegrōtant is the third person plural form of aegrōtō, aegrōtāre, aegrōtāvī, aegrōtātum (1): to be sick. Senēscunt is the third person plural form of senēscō, senēscere, senuī, — (3): to grow old, become aged. Fatīgantur is the third person plural passive form of fatīgō, fatīgāre, fatīgāvī, fatīgātum (1): to tire, weary, fatigue. (What if you chose to be angry with them who, because they are sick, (because) they are old, are fatigued?)