Nope, you cannot keep a native tree indoors, and even if you were to manage for a few weeks or months, you'd hate the result! Just because LA gets warm weather, there are many other factors that matter, and it won't work. "getting" into the 40's on occasion for a Jan. night is not going to do it either - sorry.

Keep them in now until you're sure the last frost has gone in late spring where you are, then plant them in the ground (rather than a pot) so they'll grow at maximum speed for the 'at-least' 3-5 yrs necessary to give them any meaningful options to work on for bonsai (most likely cutting them back a lot then to grow new, smaller branches, and letting the fatter trunk give the illusion of an older tree in proportion to them. Potting them up when small means you'll get slow growth at best and become frustrated with wanting something to work on (and you need to get something else -3-5 yr old nursery trees - to fuss with and learn on while you're waiting). Seeds are ok as a sideline, but not a great way to start off in bonsai, because of the time involved.