I would also slow down and look at renting or tent camping first. An older class C is likely to require not just regular maintenance, but a certain amount of "catching up" on the maintenance (many people stop doing a lot of maintenance once they start thinking about selling, etc.). If you don't do all that catching up on things that have been skipped/overlooked before you start enjoying the RV, you will likely have things go wrong during a trip. With 2 adults, those issues probably won't be a big deal. But with a baby and a 3 year old, it could really make for a difficult time.
If you do go with a class C, consider buying in the early fall. That will allow you to play catch up on the maintenance over the fall and winter. With a smaller class C, you can do weekend practice runs in your driveway over the course of the winter. That will allow you to give everything a good test run without having to suffer the consequences, figure out where and how to pack the RV, get the kids used to sleeping in it, and determine what things you need and what you won't use.
Use this summer to just get the hang of camping in general.
