חוֹשֵֹךְ שִׁבְטוֹ שׂוֹנֵא בְנוֹ וְאֹהֲבוֹ שִׁחֲרוֹ מוּסָר:
One who holds back his rod hates his son, and one who loves him disciplines him early.
אַל תִּמְנַע מִנַּעַר מוּסָר כִּי תַכֶּנּוּ בַשֵּׁבֶט לֹא יָמוּת: אַתָּה בַּשֵּׁבֶט תַּכֶּנּוּ וְנַפְשׁוֹ מִשְּׁאוֹל תַּצִּיל:
Don't withhold discipline from a youth, for if you strike him with a rod he will not die. You strike him with a rod and you save his soul from the grave.
Mishlei 29:15, 17
שֵׁבֶט וְתוֹכַחַת יִתֵּן חָכְמָה וְנַעַר מְשֻׁלָּח מֵבִישׁ אִמּוֹ: יַסֵּר בִּנְךָ וִינִיחֶךָ וְיִתֵּן מַעֲדַנִּים לְנַפְשֶׁךָ:
A rod and reproof give wisdom, but a youth let free shames his mother. Chastise your son and he will give you rest, and he will give pleasures to your soul.
Do you think Rebbe Nahman contradicted the plain and emphatic wisdom of Shlomo HaMelekh? I don't think so. I am all for following the Sadiq blindly, because I believe in his greatness which is beyond what he revealed. However, this is not a case of having to choose between what Tanakh says and what the Sadiq says, because I do not believe they contradict. I do not believe Rebbe Nahman's words about the issue meant that one should never discipline his children.
Take a quick listen to what the great American Breslov Rabbi, Tzvi Aryeh Rosenfeld ob"m had to say about the issue, also touching on these verses in Mishlei, and hear his explanation about what Rebbe Nahman meant by his words to Reb Natan:
I think this is an extremely fundamental and important point. In fact, I think it has a lot to do with bringing Mashiah, since by disciplining children and causing them to grow up into people who have a bit of yir'at kavod, you are fixing their souls. If you let them do what they please without strict discipline shaping their character, they will grow up into irresponsible, immature, spiritually inadequate adults.