P.O.
Hi D.,
I have just one daughter (10mo) and I haven't travelled with her yet (except short car trips), so I'm afraid I can't help with the baby travel advice. And I can only sympathize with what you must be feeling about leaving your 3.5yo! I'm sure she'll be fine (it's usually the mommy that has the worst time of it!)
It also looks like you've gotten some good advice about parking, but I thought I'd throw in my 2¢ anyways:
Between Remote and Express parking at the airport, if you can afford to pay for the Express, it will be worth it. I've used Remote a lot and like it, but if you are time conscious on the return, I will say that the buses come around less frequently for the remote lot and the trip is longer. There are more Express buses and the round-trip is faster resulting in them being there sooner after you arrive.
Parking at the terminal itself is good but only if you know to which terminal you will be returning. If you are fliying American, there is no guarantee! They change gates for flights like an actor changes costumes! Even if they will tell you what gate to expect your return flight to, I wouldn't trust it. However, if you are flying out of terminal B on one of the carrier with only a few gates, then it might be worth it (but it is costly... I think they have the rates on the page the other posters included in her comments).
I'm fairly good at directions and alternate routes (I've lived here all my life and did extensive travel in my job when I was younger), if you want to send me a private message about exactly where you need to get to for your daughter's daycare, I can (hopefully) give you a good route. Keep in mind that now that the extension to the President George Bush Turnpike has opened, it is fairly quick to get to Plano from DFW (if you don't mind paying the tolls).
Good luck and have a great trip!
P.
PS. I've been hearing on the news that now that there are greater restrictions on what you can carry on board with you that checked baggage is up about 20% making the wait to get your bags at baggage claim after your flight even longer. I'm sure that travelling with an infant, you will be checking bags, so just include at least a 1/2 hour into your arrival tiem for getting your checked luggage (hopefully, it go faster, but that is the average they are saying).