I have no ideas, but I am pretty sure that the kid won’t remember one way or the other if his gifts all arrived on time.
If the parents can’t handle it, tell them to grow up.
I would say, however, that a gift certificate seems like more of a gift for the parents than the kid. eToys or Amazon’s toy section could probably recommend toys by age (and if they don’t provide such a search option, they should).
I’ll agree with Lynn (and not just to kiss up, either) Having parents read to the kids can’t be anything but good for the child, and this could be something to enjoy for years. When I lived with my ex-fiance and her 4-year-old son, he loved when I read Dr Seuss books to him at bedtime. He especially liked Oh Say Can You Say so he could laugh his 4-year-old butt off at me if I messed up one of the tongue twisters.