Rabbit safe soft wood

So I'm wanting to make some toys for the girls... but I'm not sure which soft woods are safe for rabbits.

I need soft wood as this is their favourite thing to chew (along with their willow sticks). It needs to be available in different sizes & width.

Any ideas?

I used untreated pine for all my carcassing in the playhouse: can't say 100% either way but I'm sure I remember reading somewhere that it was OK.