I’m building a childs Thomas layout on a budget. Right now I can only afford 2 turnouts. So my question is would a kid prefer 2 sidings, or a passing loop. It will determine my next track purchase. Thanks in advance, Dave on a tight budget. 
Dave,
My 6 year old liked a passing loop to start. I added two more turnouts for a small (and I mean small) yard. It was easier for him to get used to operating the switches when it was a passing loop.
I guess it depends on how old the child is and their understanding of trains. Mine constantly watches several Thomas DVD’s and Engineer Dave on “Here Comes A Train”.
Mike/Nightshade
It depends what he would like, See the train going one way and then all of a sudden it taken a different route when another train goes right pass it . Or If they want to work with the train more by using the switches and droping of and picking up cars . It just depends what they like. Maybe you could ask him.
I’d set up a passing track first. You can wire it up for 2 train operation, so as to be able to park one on the passing track.
Brad
What would Sir Topham Hat do? 
Going back to my own childhood days (70’s) I would vote for the passing track. Add a siding or two later when money allows. How old is the kid?
I was 6 when I layed down my first tracks with out supervision. A simply loop with a passing siding on one end on a 4x8 table my dad made for me.
I agree. You can have Thomas sitting on the siding while Percy blows by and vice versa. It seems the younger the child, the more they want to see things move (and fast). I’m not sure a young child would appreciate the nuances of spotting cars on sidings. Well, truthfully, none of my kids (ages 28, 23 and 14) do either, but…
And, as was said, you can always add a spur or two later.
… and a passing track can be treated as two spurs anyway. When you want it to be used as two spurs, just put something in the middle that blocks the “through” aspect of it. Need it for a passing siding again then remove the block.