My son was tested at 3 1/2 with the Weschler because of developmental delays and I think his full-scale IQ was 106, with verbal being 90 something. Fast forward 2.5 years, and he had a traumatic brain injury and there was still a concern about delays, so I took him to a neuropsych who tested him again, this time the WISC IV, and his verbal score was 118 and non-verbal was 141. He said the non-verbal score is an underestimate because one of the sub-tests was timed and involved arranging little blocks (my son has pretty massive fine motor coordination issues). So no, IQ tests on a 3 year old are basically meaningless, considering how much his score went up in 3 years. Not only is the test not reliable but IQ itself changes due to development and brain maturation throughout early childhood, with some high scoring kids dropping, and others with delays going up. I'm not sure how accurate his score is at age 6, either.
My son was very squirrely with both tests at both age 3 and age 6 (for instance not staying in his chair) and was actually giving wrong answers on purpose at age 3. The point of testing at age 3 was just to rule out serious issues (like mental retardation), not to try to identify him as gifted.
