息子は野球の試合で２勝したって英語でなんて言うの？

When you win any number of games one after another, we can refer to those things happening in a row. When it is just two of them, then they are back to back.

If someone participates in a team game and the team wins a game, then it is obviously a team effort. If an individual player states that they 'won' a game, it seems they are taking credit for the whole team effort - which is obviously a fallacy.

When you want to explain that your son won two baseball matches, then you may explain this in the following ways:
-My son won two baseball matches
-My son won two baseball games back to back

In American English, the word "game" is used instead of the word "match". Match is used in British English.

If your son won two games over a period of time, the first sentence is the best way of expressing this idea. In the United States, it is common to play two baseball games, one after the other. This is called a "double header".

If your son won two games that were played one after the other, you could use the second sentence to express this idea.

examples

"we watched our son play baseball today, he
won two of the matches that he played".
or
"i won two matches today, it was fantastic".
or
"I am so happy (elated) i won two matches today".

win, winning & won
I would like to win the match
We are winning the match
We won the match

Parents are usually very proud when their children excel in anything. It is very common for fathers to be proud, when it comes to their sons excelling in sports. In these sentences, one could be bragging to others about the victory of his son and the baseball team.

"My son won two baseball matches"
a simple and easy statement implying the son had won 2 baseball matches/games.
To be victorious in something is another term used for winning, but in a more formal way.