I have a 45mm gauge LGB-based G-scale garden railway and want my grandson to have a push-along loco and some rolling stock for it. Can we make this with LEGO? The wheels need to be non-metal and have inner flanges. Apart from the gauge itself, it does not have to be to scale or be highly realistic. At his age, it's the scope for imaginative play with figures and loads that we're after.
The beauty of LEGO is that you can create virtually anything with it. I assume you are aware of the existence of LEGO Trains such as 60052 Cargo Train? The scale of these trains is not directly compatible with LGB's G-scale (the LEGO scale is sometimes referred to as L-Scale or L-Gauge) but many of the train elements can be used for building different scales. More details on the LEGO L-Gauge can be found here(l-gauge.org).
You will have to experiment a bit with sizing, e.g. how many bricks wide is G-scale track, and how do flange and thread dimensions of wheels work on G-scale rails. LEGO's assortment of train wheels is limited (only a few sizes), but you might want to check out Big Ben Bricks' Custom Train wheel collection for additional sizes.
You are not the first one to attempt this, though, a quick Google search showed several images and videos of LEGO trains running on G-scale track. Here is one recent video that I found interesting. The author's website (lgtrains.com) has more info on these trains.