Additional Study Information: This is a Phase 1 multicenter study of temsirolimus in combination with etoposide and cyclophosphamide. The study treatment is considered experimental because it is not approved by the Unites States (US) Food and Drug Administration (FDA) for treating children with acute lymphoblastic leukemia (ALL) and non-Hodgkins lymphoma (NHL) who have relapsed. The purpose of this study is to determine the maximum tolerated dose (MTD) of temsirolimus when combined with etoposide and cyclophosphamide in pediatric and young adult patients with relapsed ALL or NHL and to evaluate the toxicities and potential antitumor activity of temsirolimus when given in combination with etoposide and cyclophosphamide in children with refractory ALL and NHL.