Sleeping microenvironments (SMEs) can expose young children to chemicals of concern. Using passive samplers, we measured the concentrations of ortho-phthalates (PAEs), organophosphate esters (OPEs), and UV-filters (benzophenones, salicylates, and phenolic benzotriazoles) in the bedroom air, SME, and released from mattresses in 25 bedrooms of children aged 6 months to 4 years in Toronto and Ottawa, Canada. We detected 28, 31, and 30 compounds in bedroom air, SME air, and mattresses, respectively. SME exceeded bedroom air concentrations, indicating elevated exposure while sleeping and sources from SME contents, with two exceptions. Higher concentrations of two PAEs and five OPEs (including isomers) in mattress versus SME samplers indicated that mattresses were a source. Bedding items were likely sources of tris(2-butoxyethyl) phosphate (TBOEP) where SME concentrations were significantly higher than those in mattress samplers. Older mattresses had higher concentrations of di-2-ethylhexyl phthalate (DEHP) and benzyl butyl phthalate (BzBP). These results indicate children's exposure to a range of chemicals of concern while sleeping, at higher concentrations than in their bedrooms. Practical steps to reduce exposure include limiting items in SMEs such as toys and frequently washing bedding. Also, these results should prompt stricter regulations and greater producer responsibility regarding harmful chemicals used in mattresses and SME articles.