Final answer:
The correct conjugation is 'corren'.
Step-by-step explanation:
The correct conjugation of the verb correr for the subject 'los niños' is corren.
So the correct sentence would be: 'Los niños corren en el parque.'
'Corren' is the third person plural form of the verb 'correr', which is used when talking about 'los niños' (the children).
Learn more about Verb conjugation in Spanish