We find that if it hits 70 for a high, then shorts are best for us. However, for MVMCP, I'd strongly suggest pants. We start off with a jacket and shorts and lose the jacket during the high of the day. But, we don't stay super late, leaving in the 6-7:30 pm range normally.
We had a high in the 50's where I am the other day (and breezy) and I did need my jacket. Shorts would have been a bit chilly. However, I could have dealt with it for an hour as it warmed up. It's 53 right now as I type this outside here and I would be fine with a jacket and shorts probably until 4pm since it's sunny and no wind.
I live in the southeast (SC/GA border) and do not own a heavy winter jacket. It doesn't make sense for how our weather is. Though we get colder than Orlando, it's not long enough to make sense for me. Plus, we can have a huge range of temps in a day. So layers are our friend! On that note, even in Orlando, I'd plan on layers. I'll be taking a very lightweight fleece as well as a light windbreaker type to wear on top of it if needed. The two layers together work as well as a heavy winter jacket in my opinion when talking about temps of freezing or higher.
We leave in less than a week and will be gone 10 nights. I'm planning on 4 pants and 4 shorts and doing laundry once in the middle. And mainly short-sleeves.
As for the kids, you know your kids best! One of my kids will be in shorts every day pretty much guaranteed. And probably will rarely wear his jacket. Another one of my kids will wear leggins under her dress/skirts with the idea that she can take them off if she gets too hot. But I doubt she will, she gets cold much more easlily. She'll probably have a lightweight jacket on most of the time. My youngest refuses to wear a jacket, so we'll put him in pants and a long-sleeved shirt over his short-sleeved.