Positioning at all positions depends entirely on the game situation, i.e. number of outs, inning (late or early), type of hitter (speed, pull, slap), and fielder abilities to name just a few.
However, as a general rule basic 3rd base positioning is about 8 steps off the line (base) and 8 steps back off the baseline (approx. 24' x 24' for adults).
Double play situations require the fielder to move in helping to alleviate the difficulty caused attempting to get two players out. This is accomplished by moving to approximately 5 x 5 steps, or 3 in/ 3 over from the basic positioning.
Bunt situations are defensed by moving to a position 5 x 2 steps in front of baseline (near the cut of the grass). Finally, late game situations require a "no doubles" positioning which is accomplished by being positioned a 2 x 8 steps keeping almost all contacted balls at or toward the fielders glove side.
Variations of these positions are plentiful and are based, as stated previously, on multiple factors. These 3rd base positions work well in teaching the basics and can also be used in situations when you don't know a lot about an opponent or their tendencies. Additionally, because the size of infields change based on ages additional adjustments might also need to be made.
This system originates from the use of a 90' base path at the High school, Collegiate, and Professional level. However, as long as the player is age/height appropriate there should be very similar position results for youth fields if the step system is used over a designated tape measurement, i.e. 24' x 24'.
A few feet behind the runner when they lead off. The shortstop could loop around instead of the third baseman if you want it to be a surprise.
Fred Thomas - third baseman - died in 1986.
Fred Thomas - third baseman - was born in 1892.
Ralph Miller - third baseman - was born in 1896.
Ralph Miller - third baseman - died in 1939.
Bill Doran - third baseman - was born in 1898.
Bill Doran - third baseman - died in 1978.
Billy Taylor - third baseman - was born in 1870.
Mike Grace - third baseman - was born on 1956-06-14.
Gary Cooper - third baseman - was born on 1964-08-13.
John Davis - third baseman - died on 2002-04-26.
John Davis - third baseman - was born on 1915-07-15.