Toddlers are unpredictable under the best of circumstances. My DD is 3.5 and apparently an angel at school (albeit sometimes too curious) and a nutjob at home. She is language delayed which makes it a smidge more difficult but we are all learning.
If your family was anything like ours social interaction has been very limited over the last couple years. It occured to me the other day when we took our kids to AtHome and DD was incredibly fidgety in the shopping cart....OMG she hasn't been in one since she was a year old! Had no idea what was happening, the lights and sounds were a lot. Her older brothers at the same age were errand/restaurant pros...her...nope.
Toddlers/kids right now have had a very different experience than their older counterparts. We as adults need to remember that. Their prime time for learning out of the house social skills was largely interrupted.
Yet I think back to our WDW trip last August and DD was a champ. Our home airport is small so the wait and flight down was pretty good...snacks and the
Disney+ app and older siblings helped her stay occupied. The wait to get our bags at MCO not so great but half the kids in the airport were the same...I think most people assumed she was impatient to get our trip going. As far as the actual vacation there were only two issues and those were when the theaters at Festival of the Lion King and Philharmagic when the lights went down. We had positioned ourselves near door so DH scooped her up and off they went while I stayed with our older kids. The dark was too much...lesson learned and ride/shows where it got real dark real fast became a divide and conquer situation with our older kids. One meltdown in AK...wrapped a cooling towel around her and within minutes happy, quiet kid. And which one of us hasn't had an AK heat related hissy? Come on you know even as an adult you've been there.
Our trip was multigenerational as well. Nine people ranging in age from 3 (she had her 3rd birthday on the trip) to 69. Four kids, five adults. We didnt try to stick together, the whole trip and that was probably a really smart move. It was more of "we are headed to this park on this day" and when we were able to hit rides together we did. Met up for one large group table service meal and a couple QS along the way. The families were split into 2 hotels both along the skyliner so we often started/finished/took breaks at the same time. Used the time getting to the gondolas to catch up on what we had thus far experienced and to plan the second half of the day.
One tip I read on the boards was having your travel party/the kids in your travel party wear either the same color or themed shirts. So if one got separated which didnt happen to us (thankfully) you can look at someone else and be able to say oh so and so is in blue or a toy story shirt since everyone else is in something similar. Etsy and
amazon also sell temporary tattoos you can put a phone number or any medical info on. Embrace the stroller or baby leash if possible. Trying to walk while carrying a pretzel could slow down a runner too. After a day or so DD would grab the stroller and park her little butt in it as soon as we put her magic band on her in the morning...legit magic!
Just roll with the punches, the smiles and giggles on the little faces more than outweigh any tantrum. And honestly I felt like in WDW all the other families you encounter will have already dealt with a meltdown that day/week. As long as you are prepared and can handle the situation with some grace and humor your child will follow your lead.