A child's IQ test at very early ages like 3 is a very poor indicator of later life performance on IQ tests and has even poorer predictive power (once controlled for parents) for other things IQ is generally good at predicting. The correlation is just around 0.4 or perhaps 0.5. Some kids develop faster than others, peaking early, some are prodigys and mediocre adults, others get hit on the head.

I'm not really sure why anyone would give their 3 year old an IQ test.