I am 20 weeks pregnant and have currently left my employeer and been hired by a new company and start on the 27th. In the interview I did not disclose the fact that I was pregnant. Am I still eligible for family leave? If so when should I tell my new employer.

Both the Federal FMLA and the New Jersey equivalent require that you be employed at least 12 months with your current employer (in addition to some other criteria). So you wouldn't qualify for job-protected leave under the either federal or state laws.
http://www.dol.gov/esa/programs/whd/state/fmla/nj.htm

When you should disclose your pregnancy is a highly personal decision and not one anyone here can make for you. I would suggest sometime before your water breaks, but when exactly is up to you.

I would suggest sometime before your water breaks,

Having one of those days, my friend? :D :D :D

You could say that. And yeah, we did have an employee not inform us until she was in labor that she was expecting.