Magnolia Trees Seedlings?

I am new at growing magnolia trees. I harvested seeds from my son's southern magnolia last year and planted them, I have around 100 seedlings. My question is about when to fertilize my seedling, and if i should leave them in a cold frame or bring them in for the winter. They were planted in small pots to start, then transplanted in to larger pots. I have some that are over a year old, some 9 months, some 6 months old.

Pots range from 1 gallon pot to 4.5 . I also have 3 that came up first and are not anything like a magnolia tree. I have read that some seeds will produce freaks, well i have three. They are very different. My daughter calls them Magnolia Palm's. They are very different from the other seedlings, as seen in the picture I sent. The large one is the freak.

Hardiness Zone: 7a

PWILLOW3 from Midwest City, OK