The BASF's Kids Lab and the 12 Days of Science at Liberty Science Center (Jersey City)
Liberty Science Center is an obvious place for great kids' science stuff.  BASF's Kids Lab introduces kids to fun chemistry experiments including chromatography, strange chemical reactions with household items like hair gel, and more. Select Saturdays 10:15 am-12:15 pm and 1:30 pm-3:45 pm. Ages 6 to 11.  $5 in addition to admission which is $15.75 for adults, $11.50 for kids ages 2-12.   Call 201.253.1310 for reservations.  The Liberty Science Center will also keep your little scientists occupied during the winter break from December 22 and January 2 (excluding December 25) with the 12 Days of Science.  There will be ice cream making with liquid nitrogen, learning about polymers and how to make "snow", snowflake crafts, live animal shows, appearances by a Mathemagician and Sid the Science Kid among other events.  Free with admission which is $15.75 for adults, $11.50 for kids ages 2-12.  There may be an extra fee for certain events.

Super Science Saturdays at the Morris Museum (Morristown)
These two hour science workshops are recommended for kids 5 and up and feature some kid-friendly themes like making a kaleidoscope, examining fingerprints, and making slime.  Select Saturdays from noon to 2pm.  $10 for adults, $7 admission plus $3 workshop fee for kids.

Princeton Pi Day - March 14 (Princeton)
In celebration of Albert Einstein's birthday on March 14, Princeton goes all out with a day of pi recitation, pie judging and throwing, an Einstein Look-A-Like Contest, a science expo at the plasma physics lab, and dinky train rides with Albert Einstein.  FREE. Mark your calendars now!

Thomas Edison National Historical Park (West Orange)
Thomas Edison's inventions like the telephone, phonograph and light bulb were all perfected while he was living in NJ!  Edison's labs at Menlo Park are currently under renovation, but at the Thomas Edison National Historical Park in West Orange (his larger labs) you can tour his home, all three stories of his laboratories, watch a silent movie, and earn a Junior Ranger badge.  The park also has occasional science events for kids.  Admission $7 for adults, kids under 16 free.

The Franklin Mineral Museum and Sterling Hill Mining Museum (Franklin and Ogdensburg)
If mineral science is your thing, these two museums offer everything you could want to learn about minerals, gems, stones, and fossils. The Franklin MIneral Museum has a mine replica and a huge display of fluorescent minerals in addition to a fossil room, room with native American stone tools and artifacts, and a 3.5 acre mine dump where you can discover your own minerals and get help identifying what you find.  At the Sterling Hill Mining Museum you can see the famous rainbow room of fluorescent zinc ore as part of a tour through a real mine, and kids can collect both rocks and fossils.  Admission runs from $7-$4 plus cost per pound for minerals collected.  Call in advance because mineral collection may only be available certain days/times of year.  Special nighttime collections are organized several times a year.

NJ State Museum Planetarium and the Raritan Planetarium (Trenton and North Branch)
Aspiring astronomers will be awed by the Planetarium at the NJ State Museum which is the largest in the state!  You can see star shows for all ages, including Sesame Street One World or One Sky for ages 3-6, as well as laser light shows.  Up December 21, 22 & 23 there is a 3D performance of the Nutcracker.  Shows are $5-$6 per person.  While the NJ State Museum Planetarium may be bigger, the Raretan Planetarium has a fabulous selection of kids star shows and laser shows including The Alien Who Stole Christmas where kids can follow Santa on a trip through the solar system, Attack of the Space Pirates where a brave spaceship seeks to find alien technology while defending itself against space pirates, and Rockin' Rocket Ride where kids learn about Mr. Moon Rock and which stars are visible in the night sky, among many other programs. Shows are $6 per person and an additional $2 for 3D glasses where applicable.