Chapter 10 says Noah's sons go to various lands where they speak different languages. But Chapter 11 says "the entire earth was of one language". How do we reconcile these statements?
Various commentators interpret "the entire earth was of one language" as meaning something other than that there was only one language that everyone spoke.
But even if we assume that that is what it means, several commentators apparently noted this difficulty.
R. Joseph Ibn Kaspi commenting on this phrase says simply that it's not astounding, even though in the previous chapter it said by each of the sons of Noah "each man according to his language":
ויהי כל הארץ שפה אחת ודברים אחדים. אין בזה פלא ואם כבר קדם וכתב בבני יפת ואחיו איש ללשונו
R. Samson Rafael Hirsch explains that the two chapters are talking about two different phenomena. In his commentary to 10:5 he writes that Chapter 10 is talking about a natural phenomenon that was guaranteed to happen, while Chapter 11 is talking about an intervention of Divine Providence. He further notes that Chapter 11 speaks of saphah which actually means "language", while Chapter 10 speaks of lashon which means "dialect".
R. David Tzvi Hoffman in his commentary to 10:31 appears to understand the mentions of different languages in Chapter 10 as referring to after the events of Chapter 11:
ללשנתם. ביטוי זה מופיע כאן ברשימת העמים על שם העתיד לבוא אחר פיזורה של האנושות על פני הארץ המתואר להלן
Clearly the simplest explanation for this is that this part of the parshah is not in chronological order, like other parts of the Torah.
The lifespans of some of these children overlap with the event of the Tower of Bavel and its aftermath.
The first verse in Chapter 10 makes it clear that the children were born after the Flood:
:וְאֵ֨לֶּה֙ תּֽוֹלְדֹ֣ת בְּנֵי־נֹ֔חַ שֵׁ֖ם חָ֣ם וָיָ֑פֶת וַיִּוָּֽלְד֥וּ לָהֶ֛ם בָּנִ֖ים אַחַ֥ר הַמַּבּֽוּל
And these are the generations of the sons of Noah: Shem, Ham, and Japheth, and sons were born to them after the Flood.
In verse 25, we read of two who were born during a time when the "world split", which could refer to the splitting of the world's population after the incident with the Tower of Bavel:
:וּלְעֵ֥בֶר יֻלַּ֖ד שְׁנֵ֣י בָנִ֑ים שֵׁ֣ם הָֽאֶחָ֞ד פֶּ֗לֶג כִּ֤י בְיָמָיו֙ נִפְלְגָ֣ה הָאָ֔רֶץ וְשֵׁ֥ם אָחִ֖יו יָקְטָֽן
And to Eber were born two sons: one was named Peleg, because in his days the earth was divided, and the name of his brother was Joktan.
You would not expect Shem, Ham, and Japheth to exit the Ark and immediately have all the children mentioned here. These children were born over the course of many years. Therefore it makes total sense that the descendants of Noah's sons could travel to lands with different languages, as by that time the story of the Tower of Bavel had already happened.