A friend told me about Knex construction toys and she told me her 4 -year-old son likes it a lot, although it requires completely different building skills then for example Lego. Maybe it is more for boys than for girls although they have many girl themes as well. Knex from Pennsylvania presents themselves as the most innovative and fastest growing construction toy company. Their sets start at the age of 3 but they also have complicated sets for 9 and older. Knex is sold in over 30 countries. Let me know if you have experience with this product, I would love to hear more about it!