I would say that at least half the people that buy a camper trailer of some sort are usually trying to be budget conscious and their first trailer is never what they really wanted in the first place. I know 6 years ago when we bought our first one, the 30' fifth wheel seemed like it would be something that we could live with even though we silently dreamed of a toy hauler. Last Fall we finally realized that dream with a new Fuzion. It should be everything we ever need, but you never know. Probably the only thing that will keep me from going bigger is the need to upgraded the truck for a bigger trailer.
My neighbors on the other hand are a classic example of what you are asking. Their first trailer was a small 24' travel trailer that even though I told them they couldn't, they attempted to tow with a Nissan Pathfinder. After 3 or 4 short trips, they traded in their second vehicle for an F150 to handle the trailer. Soon enough the wife got the itch for something bigger and again they bought something that their tow vehicle couldn't handle. This time it was a 32' travel trailer that put the F150 on the ragged edge even with airbags and an additional transmission cooler. The next step was to trade the F150 for a nice F350 diesel dually. A few weeks after they got the dually I told my wife to be on the lookout for a new trailer next door. Sure enough they soon had a new fifth wheel toy hauler that challenges their dually. That trailer has lasted about 3 years so far.
I've seen this sort of thing a few times. It really is best financially if you just buy the trailer and tow vehicle that you ultimately want the first time, but people in general aren't wired that way. In some cases, maybe it is better to work your way up. That way you don't end up with a major expenditure that is a poor investment and suddenly realize that camping just isn't your thing. My advice would be if you know that camping is something you will stick with, you are not going to like a 24'-26' travel trailer for very long with 2 kids. Sleeping capacity was a major reason for our upgrade. We went from being able to comfortably sleep 4 to easily sleeping 8. Being able to take the sister in-law and her 3 kids with us to Disney last fall was a giant leap forward for us. The kids are old enough that they want to bring friends and it wasn't an option before. We look forward to more extended family trips this year!