Hello!
My DD also started to say words around 10 months, well, something like that... I speak to her in Spanish, DH in French and English while she is in the nursery.
Until she started the nursery (13 months), she was exposed mainly to Spanish as she was spending more time with me, so her first "words" where in Spanish: agua, guapa, hola...
Then, obviously, when she started the nursery, she was spending more time in an English environment, so she is picking up more words in English now (21 months).
She does not say a great deal of words, but I do not want to be concerned just yet as I think it is a bit too early. I know she does understands in all 3 languages what we want to tell her, so for her to actually speak the languages... well, it will come. We just need to keep on doing what we are doing and then help her with extra help for the reading and writing later on.
I do read to her in Spanish, watch TV ... and always talk, talk and talk. Like IFeelLike says, we do respond to her to any word/sound she makes and also try to guess and repeat the word a few times.
The other day for example, I asked if she wanted something and she said: "yeah" and I said: "si?", she looked at me and nodded and I repeated "si?" and then she said:"si". I want to believe that she understood me...
She does also say "ta" meaning "thank you" and I always tell her "gracias", which she understands, because when I give her something (like a biscuit or something) I ask her "que se dice?" (what do you say?) and she says "gracias".
DD husband does the same as I do, but in French.
Well, and many more examples, but I do not want to bore you all...
They will go through the phase of not wanting to speak because their friends do not speak the language and they do not want to feel different (in their teens...??), but eventually, if we keep on talking to them and helping them, I believe (or want to believe!!) that they will speak the language.
I think it is also very important that they know not only the language, but also the culture, the country, etc. And having friends is also essential. They can see that you talk to the parents in the same language, with the children and they can do the same, without any problem, they will not feel "different" and it will be something natural to them.
Well, I said I did not want to bare you... and here I am with my long posts, as usual...