Getting from D to A-West is maybe a 10 to 15-minute walk without kids in tow, so perhaps a bit longer for you. There are moving walkways the entire way, although in my experience people at PHL seem to imagine they are at an amusement park and either walk slowly or stand on the moving walkways. The moving walkways between B and C are located behind the row of shops on your left as you are walking from D to A-West.

The good news is that the walk is all airside -- i.e., you will not have to reclear security -- and you will clear US immigrations and customs at YYZ, so your arrival will be like any domestic arrival and you will not have to go through security at PHL. You should be able to check your bag through to MAN and you will not have to collect them at PHL. I rarely try to interline bags, but my understanding is that you can easily do this if you are on one ticket and, if you are on two tickets, you will have to show the ticket receipt for PHL-MAN to the check-in agent at YYZ.

However, the connection is rather short. It is doable if everything goes right and your flight from YYZ is not delayed, but if your flight from YYZ is late you may not make your connecting flight and your bags probably will be left behind. Can you switch to an earlier flight? I would recommend leaving a couple of hours for a transatlantic connection, just so you will not have to rush from one end of PHL to the other with an infant in tow.