Since I've had my fretless mahogany model, I've been thinking that the Ubass is a great way to get smaller children into bass playing. In my job as a community musician I work mainly with primary school kids (under 11s), and for most of them a bass guitar is just too big - even a short scale model.
I was trying to get my 13 year old daughter to play some tunes on my Fender Jazz bass a few weeks ago, and whilst she could just about manage it, she found it too heavy and also a long stretch down to the 1st fret. So she wasn't too keen on doing it again. This week she had a go on the Ubass and absolutely loved it! She practiced with it for nearly 2 hours. She did pretty good at playing fretless for her first time - the fret markers surely are a massive help. To my trained ears some notes were a little out of tune - but with practice I'm sure she can get them closer to pitch.
I'm not sure if a child as young as 4 could play a Ubass - it would depend how big they are - but probably an average 6 - 8 year old would be ok. I would guess that finger length is the deciding factor. The tension is low so they are easy to press down, it's just reaching round to the E string - try it with your son to find out!
I just weighed my fretless mahogany Ubass on our kitchen scales and with a strap attached it was roughly 2 lb, or 900 grammes. This is very light and I'm sure the weight wouldn't be a problem.
I'd recommend a fretted spruce acoustic Ubass, both because it is the cheapest model, and also because it is useful to be able to hear the Ubass acoustically for quiet practice in your armchair.
In fact, I think I may end up buying a fretted spruce model myself for kids to use when I'm running workshops.
I love my Ubass.
I did a gig with it on the prom at Grange over Sands yesterday and got a lot of interest about the Ubass from passing musicians. One guy said "Tell me where I can buy one please!". I directed them all towards Kala on the web. The other musicians said I should set up a dealership. Maybe Kala might be kind and send me a free fretted spruce model for my good advertising work. Here's hoping