I would break it down by personality traits of the child and the parents. Is there anything at home your child tends to latch onto repeatedly? Anything your child likes to do with you? Last thing you want is to spend big on stuff they just throw away... I was an intellectual child, so I tend to look for things with educational value that children will pick up more than once. However, many kids are NOT intellectual at all during those years and won't find that engaging.
Intellectual kids: Books, software
Artistic Kids: coloring books, pens, paper, craft accessories
Sporty Kids: Activity gear, balls, swimwear, swimming accesories
Social kids: outfits, figures, board games, etc
Tactile/Hands-on kids:
lego sets, figures, baking etc
Emotional/touchy-feely: figures, stuffed animals, blankets, etc.
Every child is a combination of all the above considerations.