Hi Tami,
First off, the record you linked for Johan indicates he died 29 June 1892, so he died 5 months later than father Mannes. so the question seems somewhat moot.
Regardless... here is my attempt at a transcription of the record you requested:
No. 404: Op heden den dertigsten juni achttien honderd twee en negentig verschenen voor ons ondergeteekende, ambtenaar van den burgerlijken stand der gemeente Deventer, Johannes Ribberink, oud Vier en Vijftig jaren, turfboer, en Willem Hendrik van der Wal, oud acht en dertig jaren, aanspreker wonende beiden te Deventer, die ons verklaard, dat alhier op den negen en twintigsten dezen maand des morgens te negen uur, overleden is Johan Voertman, oud vier jaren, zonder beroep, geboren te Olst en Wonende te Deventer, zoon van de echtelieden Mannes Voertman overleden en Reintje Endendijk, zonder beroep, wonende te Deventer
Waarvan wij deze akte hebben opgemaakt, welke na voorlezing aan de comparanten, door dezen met ons is geteekend.
[Signature] J:Ribberink [Signature] W.Zaalberg
[Signature] WHvdWal
I edited a Google translation of the above in order to make it (hopefully) a little more English-readable:
No. 404 Today, the thirtieth of June eighteen hundred and ninety-two, appearing before the undersigned, an official of the civil registration of the Municipality of Deventer: Johannes Ribberink, aged fifty-four years, peat farmer, and Willem Hendrik van der Wal, aged thirty-eight years, undertaker, both residing at Deventer, who declared to us that here [at Deventer] on the twenty-ninth of this month, [was] deceased at nine o'clock in the morning, Johan Voertman, aged four years, no occupation, born in Olst and residing at Deventer, son of the couple Mannes Voertman, deceased and Reintje Endendijk, no occupation, residing at Deventer
From which [information] we have prepared this document, which after reading to the person appearing, it was signed by them [the witnesses] with us [the official].
[Signatures as given previously]
As other answers have already mentioned, cause of death is not reported in the death registration - Yvette Hoitink gives some tips on researching cause of death at www.dutchgenealogy.nl
While the two deaths, being five months apart, are unlikely to share a cause, I did look at contemporary public health reports compiled by the US government (however this is based only on deaths in the "principal cities") --- there were no real epidemics in the Netherlands in June 1892 (a large Cholera epidemic came later that year) with the most prevalent diseases reported in that month being phthisis pulmonalis (i.e. tuberculosis), measles, whooping cough, and croup - combined these accounted for 272 deaths.
