That's absolutely true. When you go talk to timeshare people, they like to talk about "anyway dollars" (dollars you'd be spending anyway), they like to talk about how hotel rooms will cost more in the future, and they like to talk about how this is an investment in your family. That's really a slanted viewpoint intended to separate you from your dollars.Buying timeshares is a luxury not an investment though they try and convince you otherwise.
This is a luxury. If you can afford it and think it's a good choice for your family, fine. But go into it realizing that you'll likely never get back your initial investment, and you're committing to paying the maintenance fees every year. You're taking the OPTION of paying for a vacation and making it MANDATORY for yourself.
A timeshare can be a good deal for the right person, but if it's a financial stretch, if you have to borrow, or if you're at all unclear on what you're getting . . . then you're not the right person.
. DH is starting his 21st year on the police department. I am starting my 13th year as a full-time paramedic. We work 12 and 14 hour shifts and still manage to only need 4 hours of childcare a week for DD5 and DD7. Our daily family together time, while high in quality, is woefully low in quantity. 
I can't just book a standard room for 4 and be done with it. The world ( Disneyworld included) doesn't cater to bigger families. So planning definitely needs to be thought through thoroughly. 