What age did your child start learning an instrument (and what was it?)

Singing at 6
Piano at 7
Flute at 8

My DC started the piano at the beginning of year 2, so age 6.

My DS started trumpet at age 7. He's been playing over a year now and is going great guns. He has very severe dyslexia and is left handed (trumpet valves are operated by right hand), but neither thing has held him back. He can make sense of the sheet music but he also plays a lot by ear. It has really boosted his confidence and he loves performing.

OP, I hgly recommend reading the following books - it gives plenty of info about instruments, and ideas what is involved into learning music
www.amazon.co.uk/Meet-Musicians-Prodigies-not-Pros-ebook/dp/B005BOYXOE/ref=sr_1_1?ie=UTF8&qid=1478082473&sr=8-1&keywords=meet+the+musicians

www.amazon.co.uk/Right-Instrument-Your-Child/dp/1409138127/ref=sr_1_6?ie=UTF8&qid=1478082606&sr=8-6&keywords=raising+musical+child

www.amazon.co.uk/Raising-Amazing-Musician-child-music/dp/1860963935/ref=sr_1_fkmr1_1?ie=UTF8&qid=1478082729&sr=8-1-fkmr1&keywords=raising+a+talented+musician

Dd started clarinet at just turned 8 and has just started bassoon at 10.

I'm a music teacher and I'd say 7 is a really good age to start for most instruments. Before that, if there are any colour strings classes near you, they usually do nice singing and age appropriate stuff for younger children.

Piano at 6-ish
Euphonium at 8
Guitar at all hours of day or night

It depends as much on the child and whether they want to play it. Genuinely want to play it, not want to play it because mum/dad has sold it to them.

Dd1 started piano at 6yo, singing at 9yo
Dd2 started trumpet at 7yo, singing at 7yo.
Ds started violin at 7y, drums at 8yo.

Apart from ds with the violin they all came and asked and waited a little and asked again. Ds sort of fell into playing the violin when he saw one in a charity shop.

We had a piano at home, so age 2 DS was already wanting to play it, therefore it's hard to find a starting point. More or less:
DS1
Piano weekly lessons started at 3/4 with his dad.
Drum Kit at 6
Tuned and orchestral percussion at 11
Jazz piano at 12

DD started recorder at 4 or 5, progressed quickly but stopped age 10. Did no music for the next 2 years before taking up guitar (at age 12) and piano (age 13), initially self-taught in both cases. She's now 15 and is a pretty competent all-round guitarist and (after only 18 months of formal tuition) working on post-grade 8 repertoire on piano. She also plays a bit of sax (simple to learn for an ex-recorder player), but much less seriously - perhaps because she likes singing and you can't sing and play sax at the same time .

My conclusion is that it doesn't really matter what the first instrument is, as progress on a second or third instrument will be very rapid.

My nieces started violin aged 5, and both are in the school choir.

DS1 is nearly 15. He started drums around age 7 or 8. Began flute aged 11 and tuned percussion at almost 12. Bass guitar started at age 13. He's working at grade 6 level on all of them apart from flute, which he dropped around grade 4.

DS2 is 11. He began piano around age of 7, I think. Cello followed age 8 1/2 following a demonstration of cello and bass at school. He was too little for the mini bass so chose cello!

Dd and ds aged 3.5 Yrs and 4 yrs suzuki violin.
Second instruments at age 8.

Ferguson

That was my dd too, she saw instruments as toys and had a go at anything that was going. She's still a bit like it now.
There are tricky bits in pieces and things to learn, but if they enjoy it then it's fun and not hard work.

DS1 started acoustic guitar aged 13 and is now a very proficient player. Does A level music and plays in a band. He never showed any interest before then though did sing in the choir and did dance so creative and musical things.

DS1 aged 7 just started drum lessons and his brother teaches him ukulele. We'll see how things progress.

10 and drums
We are the least musical family

DD started piano a week after she turned 6 and clarinet a couple of months before she turned 9. But she was getting ready for formal lessons since she was a baby, my FIL is a musician so he introduced her to singing since she was a baby (all day long, she still does it), I still have these lovely memories of them singing together when she was about 2, he also introduced her to musicals, she loves them. We also listened to classical music so when she did start formal lessons she doesn't feel in a different world.

There is a great deal of misunderstanding about young children learning 'an instrument' - and sadly some parents force it on a child, or seek reflected glory for themselves if a child progresses.

Our DS started 'playing' on our Yamaha organ, at two years old; by 4 or 5 he was starting to pick out tunes, and teaching himself to read simple tunes. To him it was a great big 'fun' toy, and he absorbed music because he wanted to, and at that stage there was no formal 'teaching' or 'learning'.

DD2 started the violin at 3. For her, it was much too early, but then, she did like identifying as a violinist, so I don't really regret it.

DS started when he was 5, I think. That seemed a good age, although he isn't such a lovely player as DD2 was at the same age, but that's more to do with her being more musical.

One of their teachers once told me he started to learn at 13, and was playing with the LSO at 21. I'm guessing it wasn't his first instrument, though.

DS1: Piano at 7, violin at 10
DS2: Trumpet at 7
DD: Violin at 6

Piano and drums from age 7. Being able to read really helps. Plus reception makes them too tired to do much more than reading. It helps if they are old enough to see the link between practice and progress. Music shops sometimes have taster days when you can try different instruments. We got the piano a while before lessons and they enjoyed improvising.

I forgot to answer the original question properly...

DD1 (now 11)
Descant Recorder at 3.5
Flute (with a curved head joint) at 6.5
Treble Recorder at 7
Piano - waited until she was 10, and she is now flying with it.

DD2 (now 8)
Descant recorder at 4
Cello at 5
Treble Recorder at 7
Clarinet (much to my surprise) at 8.

The little one likes to pick out the odd tune on the piano, but is already doing enough. She does whole class trumpet lessons at school, and doesn't like them much. Both have ukuleles too.
Desc

If you wait until 7-9 years old, a vast amount of instruments will suddenly become possible. I started my two on the recorder at 3.5 and 4 respectively, and now at 11 and 8 they still play. It's possible at 4, although slow. I now think glockenspiel is a great choice for a 4 year old - it has the same layout as the piano, doesn't rely on having big enough hands, and many have the notes stamped on/ different colours, so you can invent your own notation (letter names, colour codes or just a few tunes by rote for now). I wish I'd done more of that when my two were little.

DS1 started trumpet at 8. Later switched to trombone/ tuba and is still playing at uni.

Also started piano at 10.

DD started violin at 8 and alto Sax at 9. Violin dropped after 4 years, but still plays Sax in bands at 16.

DS2 begged for piano lessons at 6, which I thought was a bit young. Gave in and he flew! Started clarinet at 7 and trombone at almost 9. He also asked to be a Cathedral Chorister at 9.

DS started guitar in year 3..