context: After four years his failing sight forced him to give this up; in 1810 he became a commission agent, dealing in oils and dry-saltery: he also acted as a steward for the Dixons of Gledhow Hall near Leeds,[8]:173 and was used by his father from time to time to carry out work for the Fixby estate (as when in 1812 he organised precautions against the Luddites).[9]:38[lower-alpha 3] He became involved in charity work in Leeds; sick visiting with Michael Thomas Sadler and organising charitable relief of the destitute.[11] In 1816, he married Mary Tatham, daughter of Mary (née Strickland, from Leeds) and Thomas Tatham, a Nottingham grocer. Richard and Mary had two children, both of whom had died by 1819.[lower-alpha 4] Early in 1820 he went bankrupt; later that year on the death of his father, he was invited to succeed him as steward of the Fixby estate, looking after a rent roll of £18,000 per year, on an annual salary of £300. He accepted, moving to Fixby Hall in 1821.[2] When in 1827 the vicar of Halifax (in which parish Fixby lay) attempted to increase his income by 'resuming' collection of various tithes which he claimed to be 'customary', Oastler was prominent in opposition.[12] He later claimed that it was this struggle that had broken his health, leaving him liable to periodic breakdowns in health.[13]
question: How many children did Richard Oastler have?
answers.text: two two two