How Many House Sparrows Are In This Box?

Hey Everyone :)

I became interested in wildlife just under a couple of years ago and shortly after I placed a couple of nest boxes up in my garden. Last year .... nothing - but this year one of the boxes became occupied (very pleased!)

I was hoping for Blue Tits but instead we got House Sparrows (however this I was pleased with as there numbers are declining) - around March time I first started seeing the male taking material in .... Anyway over the last couple of weeks I have seen the male and female visiting the box very frequently and I assumed there must be chicks inside.

Now I have a few boxes up and one is rigged up with a camera but this particular one is at the far end of my garden and thus I can't see in - so following the guidelines given on the Springwatch Easter special I approached the box casually and knocked the outside (nothing flew out which was good!) and I proceeded to open the lid and have a peak - now because of where the box is situated I couldn't look myself (it's high up as I live in an urban area and we have cats/foxes etc) I used a camera and just took a couple of short  videos.

I was in and out within a couple of minutes - put the lid back down, I didn't tamer with the chicks at all and I moved away .... I am pleased to say that the parents have gone on feeding as normal (have seen them visit many times since I checked the box) - which is a relief!

Anyway I am no expert - the videos aren't great I'm afraid due to poor light/bad focusing - but I can see 3 chicks and one unlaid egg? How old do the chicks look? Will that egg hatch? Are the house sparrows likely to have a second brood and if so, in the same place?

I am happy I have checked and will therefore not disturb the box again.

Link to videos:

http://www.youtube.com/watch?v=nng17GKROuc

Many Thanks for your time :)

Cheers, Rob