Teddimac, suzuki is a method of teaching music that is geared towards young children. There is a lot of emphasis on watching other people learn and listening to music and often the actual instrument isn't introduced for some months initially (sometimes cardboard violins are used to get posture & bowing correct etc). The music is all learnt by ear to start with and playing from memory is encouraged a lot later on as well. This means the young child doesn't need to learn to read music until much later on - critics say this means they never get good at sightreading for example, but in my experience they can do. Also, that they tend to all play exactly the same way (as on the example CDs) and without individual expression. I'm not entirely sure I agree with this either, but the sample of children I know who learned suzuki initially is admittedly very small. The emphasis on early listening skills often means they develop very good intonation skills and are usually very good at memorisation.
As all suzuki children learn the same pieces they often organise group concerts & performances which everyone can participate in and I'm told are very good.
The instrument most often taught by the suzuki method is violin, but it is also possible to learn cello, viola and even piano the same way.
To the OP I'd say don't learn piano without one to practice on & 5 is usually considered too young to start on piano - it's an easy instrument to play (hit a key & the note sounds) but the music for it is more complex: 2 clefs and several notes at once so I've heard it recommended that ordinary reading should be very good before attempting to start to learn it (around 7 is the minimum age most often suggested).
On the other hand, I think violin seems to work well started quite young although again often a child starting at 7 or 8 will catch up with those who started at 4 or 5 within a couple of years as the initial progress of the youngsters isn't usually that fast.
Ds started piano in year 3 and cello in year4/5 (first year was taster sessions only) and that worked well - I myself would go for the same/similar starting ages again given the choice - unless the lessons wouldn't be available later if you didn't take them up now.