Re: Boat Size
We had an 18' trailer sailer for many years with two children up to their early teens and a dog and cat. Had a lot of great times too. Sure 22' would have seemed luxury, and in those days 28' was enough for a couple anyway to head offshore.
Boating like camping can involve some deprivation of comfort but has other gains.
probably what the kids enjoyed most was hitting the beach and snorkeling, or cooking sausages on a fire on the beach, and having the dog along.
These days people might expect greater comfort but I would think 28-36' adequate even for older kids. After all you are not spending days at a time confined to the boat, assuming you are not going offshore and require large amounts of storage.
The advantages of smaller size are cost, and maintenance costs and time, which can eat into the actual use time. Smaller is also more likely to happen.
I would buy according to your likely actual usage. Sure in 5-10 years you may want to go offshore or maybe not. At that point you will have a clearer idea of your needs then.