Giving preschool children an IQ test designed for adults would likely show many of the test-takers with scores near the lowest standard score for adult test-takers (IQ 40 on most tests that were currently normed as of 2010). To indicate differences in current intellectual functioning among young children, IQ tests specifically for young children are developed, on which many test-takers can score well above the floor score. An IQ test designed to help assess intellectually disabled persons might intentionally be designed with easier item content and a lower floor score to better distinguish among individuals taking the test as part of an assessment process.
Preschoolers taking adult IQ tests would likely get low scores (around 40 on most current tests), while children's specific IQ tests allow for higher scores, indicating differences in intellectual functioning among young children.  IQ tests designed to assess intellectually disabled individuals are often easier and have a lower floor score to better distinguish between those being assessed.