I havent dont strickly sail, but have done this (if you make two trips dont know how far away you are) and lived downtown for a decade so will give you some ideas for activities...
Pepsi Tall Ships Chicago 2010 | Choose Chicago
plenty of diversions for an 8 y/o at navy pier, but i will say it is on the touristy side--kind of like a giant mall. the giant ferris wheel is cool and they do have an imax and stage preformers.
the art institute is world class, but may not interest the little one. field museum is neat, if you go check sue (you cant miss her) and the lions of tsavo.
for a very 'hands on' experience the museum of science and industry has a lot of interactive exhibits and is cool
the sears tower is pretty awesome and only about 5 blocks form downtown. or the 95th floor, they do a great sunday brunch w/piano, but it is on the pricey side.
, or for a real nice dinner with a comparable view to the tower :
Signature Room at the 95th - When the Sky is the Limit...
the lincoln park zoo is fun.
the shed really is neat with the main pool kinda looking like an endless pool against the backdrop of the lake.
gene and georgettis is a pretty storid steak house. if you want seafood go to joes stone crab--flown in from miami daily
the drake is a bit expensive and rooms a bit dated, but they did do an upgrade. the hilton towers has easy downtown access, the congress has better deals.
overall the city is friendly and generally safe, big but with a neighborhood feel, public transit is cheap and easy.
oh and ed dvebics is a pretty famous place, kid friendly too:
the waiters are rude and dance on the counter. its like an old old school burger joint
any specific questions just pm me