A train-obsessed toddler usually has plenty of engines already. What is often missing is more track to put them on.
A set that adds a junction, a bridge, or simply more length to an existing collection gets far more play than a single new engine, because it changes what can be built, not just what can be looked at.
A short, purposeless trip — there and back, no destination that matters — on a real train gives a toddler the actual sounds, motion and scale that no toy reproduces. Sit near the front if you can, so they can watch the driver's window.
Toy sets that include a barrier that lifts or a signal that changes are a genuine step up from static track, because the child gets to operate a rule, not just move an engine through it.
Yes — the value is the sensory experience in the moment, not the memory. It is also useful evidence for you: which parts they actually respond to.
Either works and most systems are cross-compatible with the major brands. Buy to extend what they already have rather than starting a second incompatible set.
Part of our guide to Gifts for one obsession.