There is public transit but it would be multiple changes and excrutiating - assuming you're coming off a long international flight (the 20:00 is the tip off - in the US we don't use the 24 hour clock).

Under those conditions I wouldn't even consider renting a car and driving across the City. Either check out shuttles (the JFK website will have a list of shuttle companies that operate in NJ) or consider a car service. Try Dial 7 or Carmel. The websites will give you info on pricing inluding a booster seat for your child. Just be aware that the price they quote you will not include bridge or tunnel tolls - about $20 - or the tip (20% of the fare but not the tolls).

The cheapest is to have a friend pick you up. It may also be the easiest.

What day of the week? And your flight may arrive at 8pm, but you need to add at least one hour to get off the plane, walk through airport. get your luggage if you checked it , and get through passport control/immigration. It could take longer than that too.

To be practical, arriving in the evening (from an overseas flight?) and with a child, I would want to to hire a car service like nytraveler mentions. It will probably cost about $150 with all the tolls and tip. It might take an hour or up to 2 hours if traffic is bad.

Car rentals are expensive in NYC, hard to get on summer weekends, they may not let you drop it off somewhere else without paying a very high fee. Unless you need the car anyway, it's not the best option in my opinion

There are two viable choices: Rent a car (under $100) or take a car service (perhaps $150). I'd choose the latter, but make sure you get a firm price quote from the company before committing. Try both Dial 7 and Carmel.

I agree with the others that a car service would be the least vexing!

If you feel you have to take public transportation, I would recommend taking an airport transfer coach bus from JFK to Port Authority bus station in Manhattan, then take an NJ Transit bus from there up to Tenafly.
http://www.nycairporter.com/
http://www.njtransit.com/

Note that in moderate traffic, the drive takes about 45 minutes. The public transit route takes close to 2 hours.

One other option might be to take the airport bus from JFK to Newark and have your friends pick you up there...

thank you all very much-
We're arriving on a Tuesday night. What about this airport bus from JFK to Newark? Where can I find details about it?

There is information on the JFK website. but the bus is to Newark airport (you definitely don;t want to go to Newark itself). I would check how late the bus runs (since you need to allow at least an hour from wheels down out to the street) and how often at that time of night. It might be once an hour or so and you need to allow at least an hour for the trip. Also compare the cost for 3 people to that of a car service.

Where can I find details about it?
At the link I provided for the bus service. It identifies an inter-airport service right on the home page.

And I agree with nytraveler that you then have to look at the details and make sure it works out for you.

Taking the bus to Newark Airport isn't going to help much as Newark is not really that close to Tenafly. It would probably take your friends 30+ minutes to drive from Tenafly to Newark Airport and only about 15 minutes more to drive from Tenafly to JFK (at that hour of the night). Planning on using public transportation between Newark & Tenafly will add even more time. You could easily take 4 to 5 hours (or even more) getting from JFK to Tenafly going that route.

The thing is "best" is rarely ever the cheapest or easiest and is almost always the most time consuming. I'm always amazed at how many people put cost ahead of their own convenience. I don't know about you but for my MY TIME IS VALUABLE and certainly with springing for a car service or rental car.

Taking public transportation between JFK and Tenafly is generally the least expensive way but will take "forever" at that time of the night.

If your friends can't or are unwilling to pick you up at JFK take a car service for the the least stressful and quickest way. If that does't work for you then rent a car but remember if you are not going to keep the car for any length of time you'll have to arrange to return it to the nearest rental agency location the following day and that will take more of your time and you'll still need transportation back to your friend's house or wherever you are staying. Anything else is just not worth the hassle and aggravation.

Haveyou thought about trying to fly into Newark instead of JFK and then taking a car service/cab to your friends or have them come and pick you up.

Newark would be closer and easier in terms of ease of use and customs.

The airport bus between JFK and EWR is $24 pp, and between JFK and Port Authority Bus Terminal, it's $15.50 pp. I didn't see any info on children's fares and don't know if you would have to pay for your 4 year old.

I'm generally a big proponent of airport buses as being reliable, convenient and reasonably priced, but with a young child, car service might be your best bet.

If you do want to take the bus, then you're better off going into the city to the PABT and taking a NJ Transit bus to Tenafly, as ggreen suggested. You can check the schedules into the city on the airport bus link posted by ggreen.

If you click on the NJ Transit link posted by ggreen, you can calculate your travel time and cost to Tenafly in the "trip planner" on the top left.

So the two bus option is $40 per adult - so $80 - or $120 if they charge for the child (I assume she would need a seat). Really not much less than the car service - and much more time and hassle.

Thank you all again. You are very helpful and know your way around...I'll think it over and get back if I need more info

No, they would take either the $24 JFK/EWR bus OR the $15.50 JFK/PABT bus, not both.

From EWR they'd have to figure out how to get to Tenafly.

From PABT they take one bus to Tenafly, at a cost of $5.50. Total cost per adult is $21. Presumably there is either a reduced fare, or no fare, for the child on the airport and NJTransit buses, so it's considerably less than car service.

To the OP, bear in mind that just because Newark is in NJ doesn't mean it's much more convenient to get to Tenafly from there. Unless your friends pick you up at EWR, you're much better off going into NYC and getting the bus from there.

The trip planner on the NJT website shows a travel time of 30-40 minutes from Port Authority in NY to Tenafly at approximately 10 pm and thereafter.

Yes, panecott makes a very important point, Tenafly is actually a north of the George Washington Bridge and Manhattan, while EWR is southwest of Manhattan, which is quite a distance from EWR. You are probably better off coming into the Port Authority in Manhattan and taking a different commuter bus from there to Tenafly.

I agree that the 2 bus combo to Newark airport makes little sense. I think the original suggestion was to take one of the services that shuttle between the 2 airports JFK/EWR (like this one http://olympic-limo.com/schedule-airport%20transfer-ewr%20jfk.html ) so that only one bus is necessary. Still not the best idea IMO, but at least it doesn't involve switching buses in midtown with suitcases and a small child!

Harel said "I'll think it over and get back if I need more info" so I think he's got the idea that there are options, and then there are better options...