。
Spare the rod and spoil the child.
Literal
Whip [obj-を] begrudge [if-と] child [topic-は] no-good becomes.
The Japanese version of the English proverb 'spare the rod, spoil the child.' 惜しむ ('to begrudge, be reluctant to use') + ~と conditional sets up the cause: 'if you hold back the rod...' 駄目になる ('become useless, go bad') delivers the consequence. The proverb form with ~と + result is very characteristic of Japanese sayings.