My kids each were really young on their first trip (prepping for runDisney is how I lost the weight from my pregnancies). When were took my oldest the first time, he was 11 months. My youngest went on her first trip at 12 weeks. He enjoyed his first trip, but all we did was 2 park days. His 2nd trip at 20 months, he really loved. Still only 2 park days, but also loved the pool and meeting Chip and Dale at the campground. It wasn't until he was 3 that we had a rough trip with meltdowns. When I was a kid, our only trip was when I was 9, my brother 8, and my sister was 5. She doesn't remember the trip, but I remember both she and my brother had a hard time with the walking, heat, and long days, but we were at an offsite hotel and did 4 park days in a row. So I guess it depends on where you stay, the kid's personality, how you schedule your days/week, and if you are ok with them not remembering it.