I have done a search at IGD/PRDH. I can find no Antoine Legault b. 1852 in Chateauguay. I did find the parents, Jacques Legault and Delphine Gourgon dite St-Maurice.
The parish register entries for that family are:
Jacques and Delphine married 1842, St-Eustache.
Jacques remarried Marguerite Provencal 25 Jul 1881 Montréal (Notre-Dame-de-Montréal)
Children (Jacques and Delphine):
Delphine Legoth, b 31 Mar 1843, St-Eustache; m Pierre Sauriol Sansouci 29 Jul 1861, Montréal (Notre-Dame-de-Montréal)
Edesse Legaut dit Deslaurier, b 18 Feb 1845, St-Benoit; m Elie Adam 29 Jul 1861, Montréal (Notre-Dame-de-Montréal)
Marie Legaut dit Deslaurier, b 13 Mar 1847, St-Benoit; m Philippe Parys 3 Nov 1863, Montréal (Notre-Dame-de-Montréal)
Jacques Legault, b 26 May 1849, St-Benoit; m Georgiana Therrien 30 Oct 1871 Montréal (St-Enfant-Jésus-du-Mile-End)
Eloise Legault m Damase Ouimet 28 Apr 1879 Montréal (St-Jean-Baptiste)
Aime Legault m Rose Amanda Lacoste 1 Sep 1890 Montréal (St-Enfant-Jésus-du-Mile-End)
I manually looked through 1852 Chateauguay and did not find any Legaults.
Then I searched for Antoine Pierre Legault with 1840-1860, no location and found an Antoine Legault b 1845 St-Benoit with father Jacques and mother Marguerite Trottier.
Are you positive about the parents names, and birth date/location?
edit....
Found another child:
Felix, m Mathilda Therien 26 Jan 1874 Montréal (St-Joseph)