young tomato seedlings eaten

Mine are only just at that stage - first proper leaves, or very slightly more, but I wouldn't consider having them in the gr'house for ages yet - far too vulnerable, and not consistently warm enough for them.
Perhaps it would be better to sow later @thriftybri. They need plenty of light early on, so the further north you are, the less daylight hours in late winter. I don't sow until around mid to late March, and sometimes later.