Learn Italian: C'erano i miei vecchi giocattoli sul pavimento.

C'erano is the imperfetto (past tense) form of ci sono (there are). We use the plural c'erano meaning 'there were' because it refers to multiple things: i miei vecchi giocattoli (my old toys). If there was only one toy, you would use the singular c'era (there was).

Why does the adjective vecchi have an 'h' in it?

The singular word for old is vecchio, which has a hard 'c' sound (like a 'k'). When changing it to the plural masculine form vecchi, Italian adds an 'h' to keep that hard sound. Without the 'h', it would be pronounced with a soft 'ch' sound.

Why is there an i before miei? Doesn't miei already mean 'my'?

Yes, but in Italian, possessive words almost always need a definite article before them. Because giocattoli is a masculine plural noun, you use the masculine plural article i to make i miei. The main time you drop the article is for singular close family members, like mio padre (my father).

How does the word sul work in this sentence?