There are quite a few species of Horse Chestnut or Buckeye (same genus) in cultivation, but most would still have green leaves now.  The California Buckeye tends to be a smallish bushy tree (but it can get big) and tends to loose it's leaves when the weather has been hot and dry for a while (i.e. now).  In fact one objection to it, is that it is often bare or brown in summer.  The flowers vary from species to species (in color, shape, and how they are arranged on the inflorescence), and if you can't figure out which species from the leaves or fruits, the flowers should help.  Some of the California Buckeye trees (depending on where you are) may begin to flower in winter after rains start up, but the other species usually wait till spring (around April to June, depending on species and climate).
 
The main reason I sent this note though is about the seeds.  While they are not particularly dangerous usually, som! etimes children will think they look good to eat and chew one up.  They are poisonous and can be dangerous if eaten in this way.  I'm not sure, but I think if swallowed whole they just slide through and out the other end without much danger.  Poisoning seems to be pretty rare though, and they are planted a lot because they are pretty trees with pretty flowers.
 
Dave Ferguson
RIo Grande Botanid Garden
Albuquerque, NM