The three senior ministers condemned chancellor George Osborne’s proposed policy, which will hit tens of thousands of stay-at-home mothers.
The ministers revealed their concerns about the changes in benefits to Daily Telegraph reporters posing as Liberal Democrat voters.
The ministers also revealed efforts to slow or stop Tory policies.
Scottish secretary Michael Moore described the child benefit decision as “blatantly not a consistent and fair thing to do”.
Business minister Ed Davey said the announcement had left him “gobsmacked” and said it had been “dreamt up out of the blue”.
Pension minister Steve Webb said he had written to the chancellor to complain about the policy because the details were “not right”.
The three men also voiced fears about other Coalition policies, including housing benefit reductions and the tuition fee increase.
It is the first time that Liberal Democrat concern over child benefit cutbacks has surfaced, with opposition to the proposal previously coming from back-bench Conservative MPs.