mae clustiau mawr gan foch bach

• mae clustiau gan foch bach, mae gan foch bach glustiau mawr, mae gan foch bach glustiau

Literally "Little pigs have big ears".

mae clustiau mawr gan foch bach

1. (idiomatic) little pitchers have big ears (observation that small children often overhear more of what is said than adults realize or desire)

• R. J. Thomas, G. A. Bevan, P. J. Donovan, A. Hawke et al., editors (1950–present), “moch”, in Geiriadur Prifysgol Cymru Online (in Welsh), University of Wales Centre for Advanced Welsh & Celtic Studies