"I opened the door and my children were in the house."
Translation:D'oscail mé an doras agus bhí mo chlann sa teach.
Verbs have dependent and independent forms. The dependent forms depend on the presence of a verbal particle, such as an or ní or go (or their past tense equivalents).
For most verbs, the dependent and independent forms of a verb are the same, but for some of the irregular verbs, the dependent form and the independent form are different.
raibh is the dependent form of bhí. fuil is the dependent form of tá.
Bhí mo chlann sa teach - a straight statement, with no verbal particle, therefore the independent form of the verb is used.
An raibh mo chlann sa teach? - the interrogative verbal particle An requires the dependent form of the verb - An raibh?.
Ní raibh mo chlann sa teach - the negative verbal particle Ní requires the dependent form of the verb - Ní raibh.
(The verbal particle An eclipses and the verbal particle ní lenites, but neither of these processes apply to a word that starts with r, like raibh).