I have a two year old son who has had a strong maple syrup odor intermittently throughout his life. We just received negative test results back for two blood tests that were organic urine acid, and branched-chain amino acid (BCAA)- which is used in identifying maple syrup urine disease. He did have a perfectly fine Newborn Screening at birth and I did breastfeed my son the first year of life which is thought to have kept most symptoms at bay. There are different forms of this disease- classic, intermittent, intermediate, and thiamine responsive. With the intermittent form a child can be of variable age when onset of the disease occurs. Also, they can have the maple syrup odor off and on, normal early growth and development, episodic decompensations that can be severe. The child can have normal BCAA blood levels when well, and when the child is sick they can have BCAA levels like in the classic form of the disease. So, if the child is tested when they are feeling well, there is a chance the test will come back perfectly fine. My advice is to seek the opinion of a pediatric metabolic specialist and as soon as you notice the maple syrup odor or your child is sick in any form; run to the lab and get the tests right away to avoid a false negative result. I am currently waiting for my son to wake up one morning with the strong odor of maple syrup so I can get the blood work done immediately after. My pediatrician agreed to this since I brought her evidence of the odor on my son's warm sleeper pajamas. It seems that he sweats badly at night and the odor comes through his sweat- when the levels are expectantly high at variable times.
Check out this very technical webpage: http://www.ncbi.nlm.nih.gov/books/NBK1319/
I hope this helps. Take this seriously, even if it doesn't seem to be serious at the moment, it can be at a later time (with the forms that occur at variable ages and left undetected unlike the classic form).