Engineered nanoparticles (ENPs) are the building blocks of novel materials and consumer products that hold great promise for our societies. When ENPs are released to the environment, however, they can induce irreversible processes that can affect human health. To ensure safety for all nanoparticle-based products throughout their life cycle we urgently need to develop techniques for determining their toxic effects and the exposure levels of humans to ENPs. In an attempt to estimate whether nanotechnology can threaten more sensitive parts of the population such as children, we provide a brief overview of the potential pathways of introducing ENPs into the environment and the state-of-the-art techniques for assessing human exposure, as well as our current knowledge on their toxic effects.