It is true that you will want a relatively low trail number because of the lower speeds most kids will reach; however, you have to remember that trail is dependent on wheel diameter as well so it is expected that it will be quite a bit different than a big with twice as large wheels.
There are many prominent brands that use a fork offset of zero on their 14" learn to ride bikes with head angles around 70. These bikes can be very squirrely at speed but are great for learning. If this is intended to be more of a ripper bike than I think you are definitely on the right track.
When designing kids bikes (and adult bikes), I find it helpful to compare geometry of different frame sizes through ratios. For instance, look at the ratio of trail to wheelbase as compared to your preferred geometry and size to get a better understanding of how the handling will compare.