Since you have toddlers and car seats anyway, it may be better to have a car in Philly, that way you know your kids will be buckled into their seats. cant see how that would work out with uber or a taxi. I would value safety over the cost of parking, and moving the car.

call your hotel in nyc ask if they anticipate any street closings, or problems unloading in front of the hotel. ask about the parking, do they have valet service or do you have to take the car to a garage. it wont be cheap but
I am guessing you already know that.

you can ask if your rental car will have ez pass. as it will make it faster for the bridges toll roads and tunnel

the drive is about 2 hours, those who say less never figure in construction and traffic. and it can take longer given the congestion at the tunnel on the nj side, day of the week and time of day will make a difference, and once you are in Manhattan it can take some time to get to your hotel depending on traffic.

there are rest stops along the way.. full service if you need to change a diaper, or whatever may arise.

Driving will take 2 or 3 times as long as taking the train and you will have to pay for tolls, gas and parking for each night and each time you park the car. Expect parking in NYC to be about $50 per night. Last time I was in Philly it was about $30 or so.

Parking at the St. Regis is $70 or so per night, plus tax.

We are taking the car from Philly to NYC and then dropping it off in NYC. We won't keep it in NYC - I think my two toddler boys will love taking all the taxis, subways and trains while we are in the city. So, we are literally just using the rental car to get from Philly to NYC. Plus, our hotel St. Regis, charges $70 a night for parking.

I suspect that living in a more car-centric part of the country is impacting your decisions, and making a challenging trip even more challenging.

If you forget about renting a car to get from Phila. to NYC, you can leave the car seats at home, which cuts down on stuff you need to drag along immensely. I haven't rented a car at PHL, but I suspect getting 2 kids and stuff from the terminal to the car isn't going to be easy, for one thing.

I don't understand why the train schedule is difficult. 30th Station is huge and pretty interesting, and it has bathrooms and lots of food choices. You don't even have to wait in a long line (and go down stairs to the platform) to board--go the the Red Cap counter and a porter will take you and your stuff down in an elevator when the train arrives, and before others board, and place it on the train. All for the cost of a tip.

It doesn't make any sense at all to rent a car just to get between Philadelphia and NYC.

With two toddlers, luggage and other equipment, it can make a lot of sense to rent a car.

Rental cars are such a pain when traveling. It's just a giant pile of metal you have to care for and be worried about. You're on holiday, you want the least amount of things in your mind possible.

Also, Philly and NYC is not really the type of place you want to experience on the road -- drivers can be a bit...rushed to say the least.

Embrace the train life!