Ethel M. Botanical Cactus Garden decorates with multi-colored lights for the holidays, it's beautiful. There are paths through the cactus garden, they have a gift shop with M&M merchandise and a shop to sell the chocolates. Google Ethel M's and you can get an idea of what the place is if you don't already know.
There is parking available, but it gets extremely full and there may be a walk of a half-mile to the Cactus Garden, so plan for the time. If you miss the group, enjoy the Cactus Garden anyway. We won't necessarily tour the garden as a huge group anyway, it's a public space. Bring kids, Grandma, friends, family, anyone who can walk a bit.