Mine are onion sets Zoe, seeds are different, though I would love to know how growing onion seeds works!!! Anyone?
Onions from seed are really easy - and no worries about running to flower / seed. And as the traditional time to sow is Christmas Day afternoon it gives you a great opportunity to get out of the house for a few minutes - though you are fine sowing up to about mid Feb.
Here's a little clip on planting plants produced from seed...