Not 100% sure how they'd do in planters but Cornus would provide winter colour without being evergreen and snowberry would attract birds in winter. Buddleia will grow just about anywhere and is great for butterflies.

I'm thinking along the lines of encouraging wildlife so that you can get the children interested. And I wouldn't worry about poisonous plants as it's a great opportunity to teach children about not eating what they don't know (a lesson they might not get at home).

I'll leave others to make suggestions but I've a red robin in my front garden and it does not like the wind one bit.

Hebes? With the proviso to check if they're hardy before you buy them!

There is a bamboo you could use - I planted some as a windbreak 5 years ago, it gets plenty of sun and plenty of wind and its still trying to take over the universe - Phyllostachys nigra or P. aureum. There is a drawback though - where you are, the roots will be vulnerable in pots to cold winter temperatures, and the pots may well blow over in strong winds, though that's true of any tall plant in a windy area.

Photinia is not a good choice for this kind of situation - it prefers a sheltered position, and the cotoneaster is toxic if eaten, including the berries.

As I'm busy telling you what you can't have, here's a suggestion for what you can - but it only works if the measurements of the pots you've given mean .05 wide by 1m deep. I'd go for holly - its obviously prickly, and that will discourage children from trying to eat any berries it produces, though most children understand that holly isn't edible. Even if they did eat the berries, they'd have to eat quite a few to have vomiting, they're not so toxic as cotoneaster. As for varieties, Ilex 'Green Pillar' is a female plant which produces berries, if there's a male plant nearby. Ilex Silver Queen is slow growing enough to keep in a pot for a number of years, and is a male plant.

I know you said you'd prefer not to have something prickly, but the situation you're describing is a difficult one to find plants for - they need to be hardy, not prone to being killed through the roots by cold, particularly given you're in West Yorks, wind resistant and not toxic, or particularly toxic - Holly fits all the requirements, barring the fact its prickly...

On the other hand, if your pots are wider than they're tall, then you're restricted to much lower growing plants...

I know you wanted evergreen but would it not be a good idea to have a mix of deciduous and evergreen that way they would learn about the two types and see the differences. You could then grow fruit trees in large containers or Blueberries and Blackcurrants etc.