We [topic-は] summer-vacation [object-を] yearn-for-are.
待ちこがれる ('to yearn for, to wait anxiously for') is a compound verb: 待つ ('wait') + 焦がれる ('to pine for, to burn with longing'). The 焦がれる element carries intense desire. Stronger and more poetic than just 待つ or 楽しみにする.