I invariably have problems with machine feet that have little metal guide bars on them, including my 1/4" foot. My favorite machine foot has indicators on it (both right and left); I use those as guides and always get an accurate 1/4" seam allowance.
Recently I did a quilt for a toddler. It was comprized of 25 11-1/2" blocks (with a ME design centered in each). I cut the sashing 2" wide and with 1/2" seams, the allowances butted up against each other exactly. Everything fit together very snug with no unwelcome seam allowance "lumps" or "vacancies". It is my opinion that ... if it is feasible depending on the quilt pattern ... the wider seam allowances on a small child's quilt give it an extra bit of sturdiness for what is likely to be a really active lifestyle for the quilt.