We bought fun kids gifts at Pylones. They really liked them. There are several branches in Paris, though we went to the shop in the shopping arcade of the Louvre.
Yes, a fun store. There is one on Ile St. Louis also.
It's an international chain with locations in many different countries. Sadly all of their US locations were permanently closed last year.
http://tinyurl.com/h4dm2sy
Another growing chain with cheap gifts for kids is Tiger/Flying Tiger:
Love Pylones! They have great things for adults, too. All my friends give me wish lists of what to bring them back when I go to Paris.