I bought my daughter her first pony when she was 13 months old, a little 34" Shetland with 6 month old foal at foot... Obviously we were going to sell the foal to get a bit of money back - but never did
My daughter had the best experience ever growing up with her little ponies. Because they were her size she was able to do lots with them from a very early age. They were (are!) little poppets - I insisted on good manners from the start as they were children's ponies - so DD could groom them, and soon she was helping to tack up, bath them etc. By the time she was 4 she could do pretty much everything with them, including mounting from the ground and riding off the lead. She did her first season showing off the lead at 5, and I have wonderful photos of her happily cantering her little pony across Ainsdale Sands (a huge beach going on for miles in all directions for those who don't know it) when she was about 5 yo.
Yes she outgrew the ponies sooner than she would have outgrown a Welsh A or Dartmoor. But she loved having ponies her size and being able to do so much with them. It also didn't hurt so much when she fell off them, being so close to the ground! At 9yo she is now a very competent young horsewoman - not just a rider - who loves having ponies to love and groom and look after as well as ride.
And the mini ponies? Well they're out in lovely long term loan homes doing the same job for some other lucky children!
I'm really glad I've asked and had all these opinions/stories as some of the points made I hadn't considered 
Hi Amber1012!
My daughter is 3 in November and we bought a little Shetland when she was 18 months. She doesn't really ride much at the moment but 'Strawberry' our little Shetland is fantastic to do round on the yard so she's already doing her job & giving Isla some confidence
Strawberry can be a very whizzy little thing and she's strong so we do have to be careful but she's really good with Isla so we're happy with her!
My niece had a little caspian pony years ago and he was a lovely little pony but very sharp - my niece was an accomplished little rider at the time so they were perfect for each other but I wouldn't have liked to think a novice would have been on him.
We've had lots of welshies over the years and they've been great but again only 1 was suitable for a novice (I actually tried to trace this pony to buy him back for Isla before we got Strawberry!).
Good luck pony hunting
You'd be surprised JLD. My friends daughter on my 13.1 at the weekend. She is 5. We did a two hour hack including road work (she has her own pony too but he is hot to hack in company, she has good facilities so rides in the arena off the lead rein a lot so is at least as competent as my daughter).
She's a big chunky 13.1 as well, I ride her too
but I'm hoping to borrow a little pony for that... there's always people around with tiny ponies who need jockeys so perhaps ask about? Although I guess you still need a pony at home for him to play with. If I had to buy one, I'd probably get a little new forest. Welsh A's are lovely but they can be a bit sharp.
Photo overload alert!!!
I have thousands of photos of my little ponies with my daughter and her friends, but will limit myself to a small selection showing just how much fun little people can have with little ponies...!
The ponies are mum (grey) and daughter (dark brown). As you can see, daughter is a lot more laid back than mum!
Of course it's not only little Shetlands that make wonderful kids' ponies. We also have a little Welsh A, now almost outgrown but a fantastic confidence giver - I've lost track of the number of kids who've had their first canter / done their first jumps on her over the past few years. She'll be with us for life as she has had health issues, and I have a queue of kids wanting to ride her!
Now look what you made me do. Lovely pony on my local pony club website. Not sure I can afford a pony ATM and coming into winter now and daughter onky 2 which id said was a little young. Very dangerous thread!!!