If they are tall and leggy and falling over there is two reasons for this, lack of light or damping off.
Lack of light will cause the plants to stretch upwards seeking out light, they will compete against each other for this and become leggy, once leggy they have no strength in their stems to hold them up.
If they are only very, small i.e. 1/2cm then it probably is damping off caused by a virus. Pots not washed properly from previous seed sowing can carry the virus, in future wash pots thoroughly in hot soapy water with a dash of detergent to kill virus' present.
Don't loose heart, all gardeners suffer from these issues for example i'm on my second sowing of parsnip seeds and still trying to get them to germinate - I'm not disapointed or frustrated as I know how tempermental they are to germinate and they take a long time, eventually Ill get some going.