Little Mushrooms In My Seed Trays.

Hello,

I'm new to gardening, sowing, potting, etc, I do find it very therapeutic.

However, I have a problem, at least I think it's a problem in my 4 tier greenhouse I have planted some seeds in trays, some of the seeds are coming up great, yet I also seem to have some tiny mushrooms too.

Is this a problem?

Have I done something wrong?

Will it affect my seeds/flowers?

Many Thanks in advance.

John.