Sorry but my knowledge of Video Converters is tantamount to zero. However I have done a little Googling and established that Freemake is good but care must be taken when downloading the programme because it is offered as a free item but along with a lot of extras, such as unwelcomed Toolbars.
http://download.cnet.com/Freemake-Video-Converter/3000-2194_4-75218346.html
Incidentally, you are correct to mention that 'Movie Maker' is no longer available for Vista. However, I would have thought that it was installed in your computer when you bought it.
Another thought is that perhaps the Video Clips of your Granddaughter could have been sent to you as E/mail attachments and your comp's inbuilt Windows Media Player could have played them one after the other; because the legality of saving from You Tube is somewhat questionable.....Not that anyone would be aware that you had.....Except perhaps Google of which I think You Tube is part of the Google Organisation.