You are going to have fun with this. The information won't be hard to work out. Some things in you favor are a relatively uncomman last name and a situation where the people are mostly in one location and South Dakota has a number of records online.
I went on Ancestry and easily found a number of records. In 1910 Steven is with his parents Louis and Millie Hardina in Marshall County SD. Louis is listed as born in Hungary (Bohemia) and Minnie was born in Minnesota. Their children in order of birth are Richard age9 Born in SD, Mabel 7 born Minnesota, Stephen 5 born MN Charlie 3 born SD and the bonus is that also with them is Frank Hardina father age 67 forn Hungary (Bohemia). Frank and Louis are born listed as having immigrated in 1877.
In 1900 Louis and Minnie were newlyweds living also in Marshall County. The 1900 census is significant because it lists month and year of birth not just age. Louis was born in Aug 1873 and Minnie in Feb 1878.
The South Dakota birth index has Richard's birth in it and lists his monther as Millie Wanous.
The South Dakota marriage index shows Mabel Hardina married Freddie Ellestad in Dec 1924 so you should be able to follow her.
The SD Death Index shows Frank Hardina died 23 Mar 1913. and Louis died 22 Aug 1951.
This should give you some clues to get started. Ancestry is the easiest and you can either sign up for a 2 week trial or most public libraries have it available. You can also find records on the Mormon website familysearch.org and on the South Dakota genweb site for Marshall County.
On Ancestry there are several trees that include this family. One of the most complete is likely made by a descendent of Steven's brother Charlie. These trees can be good for clues (but do check the information!) and links to websites the owners have already found and for making contact with relatives who can be a great source of information. It is amazing how quickly family information can be lost. Talking to relatives you know is another good place to start.
Hope that helps,