Exactly.
It's going to be tight, very tight.
But here's the good news!
1) YYZ expects that you will miss your flight -

- so, you won't have a problem at the desk trying to re-book. Now, if the next flight is full, you could have a problem. So be prepared, look at the flight schedule, and write down the flights that would be acceptable to you and your family - before you go.
2) Get a porter.
Get a porter.
Get a porter.
The golf carts are fine, *if* the one you've asked for through passenger assistance shows up. If it isn't right there, get a porter. Let him grab your bags, count them, (and the kids!!

) and then get ready to run.
And seriously, we mean run, if you want to stand a chance of making this.
3) When you get to the cattle call of a line-up in YYZ that is USC&I, make your presence known to one of the agents (they're usually scattered through out the crowd)
All you have to say is "Flight #___ to Orlando, 4 people, travleing with small children...and they'll get you to the line up you need to be in.
As well, your porter should direct you right up to one of the agents, but he may not.
So you have to be prepared to take charge.
Tell your partner to stay with the luggage and kids, find the agent, tell them your spiel, and run back and get your partner, kids and luggage (and the rest of the people from your flight, also connecting to MCO will probably be right behind you!

)
4) Once you're through Customs, it isn't over...there is a desk by the luggage belt, and if your flight is departing in the next 5 minutes, tell them, ask which security line to get in, can they call and ask the gate to wait for you? and hope for the best.
Have I scared you enough yet??
I'll be honest, and tell you that it isn't fun. We've missed it more times than we've made it.
Stay cool, be prepared, pack as lightly as you can, put all your electronics in ONE bag, so you'll only have to open that one..wear slip on shoes if you can, and skip wearing a belt.
If the kids have a favourite blankie or toy, get one of those harness/elastic thingies, that they can attach it to their, or your, wrist.
Remember, you will get to WDW, just maybe not on the flight, or route that you originally booked.
HTH!