Thalys from Paris to Amsterdam- arrival time at Paris train station

With your large group, I'd want to arrive at least 30 minutes ahead. You may not be able to find your track number any earlier than that. But once its posted on info boards, it's usually available to board. Gare du Nord is a simpler layout than some other Paris stations but it's undergoing renovation, so there could be detours inside. It's also famous for pickpockets so beware any distraction, keep your valuables tucked away, your hands on your luggage, and your group organized.

If it was just you, I would say you need to be at the platform 15 minutes before departure, they have a bag x-ray system they use as you enter the platform. Certainly not more than ½ hour, as they don't post the platform number until about ~20 minutes before departure. Add 5-10 minutes to get from the street or the mètro.

When I was at Gare du Nord a few weeks ago, I noticed a queue waiting to be let onto the platform for a Thalys train, they hadn't started putting their luggage through the X-ray machines so everybody was just waiting in a queue, and it was about 15 minutes to departure. People were still joining the queue.

But, you are "herding" an unspecified number of children. How are you all arriving at the station? And how long will it take you to get them off the bus/métro and through the station (about 200 metres), and check for stragglers? Only you can say.
Make sure everybody knows the train details, number, departure time and coach and seat numbers (I assume you have a block of seats in the same coach), and make sure they get on the correct coach, and don't get on at the wrong end, walk through the train and cause chaos.

I'm thinking about taking a train from Paris to Amsterdam next April.

How long is the journey? Should we fly? I don't want to spend 6 or more hours on the train. It seems flying would be more efficient and possibly quicker. I know you have to factor in the time you spend getting from your hotel to the airport, etc.
Do you think flying is the best option? Which airport and airline do you recommend?

Thanks!

It is only 3 hours and 17 minutes on the Thalys. Flying would take a lot longer city center to city center.

Judy B - my tickets say 3:15 journey. That's better than spending time riding to the airport early, going through security, waiting around for your flight, and then having to take the train to Centraal from AMS. PLUS, we don't have to worry about not carrying miniscule sized baggage like many european airlines require. We are making this train journey this fall. I'll let you know how it turns out.

Sam and Nance,
Thanks for your responses. I agree the train makes more sense given the time frame is 3:15 hours. This is perfect as a friend has told me that the train goes through some pretty scenery, too.

Thank you Laura and Chris!

Pretty scenery? No. Mostly flat fields and urban grot.