"Visit grandparents" can be translated as "看望外祖父母" in Chinese.
Source: This phrase is a direct translation from the Chinese to Engpsh.
Example sentences and their translation:
I'm going to visit my grandparents this weekend.
我这个周末要去看望我的外祖父母。
She spends every summer visiting her grandparents.
她每年夏天都会去看望她的外祖父母。
He never forgets to visit his grandparents every month.
他每个月都不会忘记去看望他的外祖父母。