Did someone mention two of my favourite words???
Well, in a nutshell they do, IMHO, provide the very best music experiences for young children. (However, both can be studied to the highest, conservatoire level and I'm always keen that they should not be seen as approaches 'just for children'!)
The bad news is that it's almost impossible to either get a full understanding of what the whole approach is about, or how to teach it, from a book.
The Dalcroze Society is VERY wary of putting much down on paper, purely for the reason that people could go off, follow a couple of lessons slavishly without real understanding, and then pronounce themselves to be 'Dalcroze teachers'. They take a very dim view of people advertising themselves as Dalcroze teachers unless they have done the Certificate. At present I believe you can study for this over two years and it consists of two weekends per term (currently held at a school near me in Sunny Croydon). I know several people who are doing it at the moment who travel considerable distances (dark corners of Kent, Norfolk, the North-East etc) and stay over on the Saturday night if the travel is too far.
To be successful teachers of either approach requires a considerable amount of experience and training - however, this is not, of course, to say that you can't start to learn some of the ideas and techniques and start to try them out with your students!
The Dalcroze Summer School is either next week or the week after, I believe. It's held in Canterbury (Christ Church) and I think the basic course is Mon-Fri although there was an option for two extra days, I think. They do have an open day when anyone can attend any of the classes so if you could get to that it would give you a taster and also you would be able to look at what books they have available.
Off-hand I can't remember the website but if you Google 'Dalcroze Society' it will come up and give you an e-mail addy for the administrator.
The British Kodály Academy also runs a Summer School (12th-19th Aug in Leicester) and courses throughout the year. There are two very good weekend courses in Godstone, Surrey (just off J6 of the M25) in November - one for Early Years and one for KS1/2 (I'm teaching on the latter). I run evening classes which are not specifically for the teaching of it, more for the development of your own musicianship using the Kodály principles (very necessary so that you know where all the early work is heading). Again I have students who come quite a long way - they are very dedicated! One of them comes from Herne Bay to Croydon and is also doing the Dalcroze certificate *phew*.
If you want to know any more details about any of these courses please just PM me.
Regarding books - as I said, there's no substitute for courses - but Lois Choksy's 'The Kodály Method 1' would give you an overview. It's a USA publication (Prentice Hall) and VERY expensive but you might find it second-hand or in a library. Lucinda Geoghegan's 'Singing Games and Rhymes for the Early Years' (there's also a Middle Years book) are excellent collections but don't really go into the approach itself.
One of my Big Plans

should start to come to fruition early next year and may be of help to you - again please PM me for details!
Finally, I'm always very happy for anyone to come and observe my classes. I teach in a state primary in Kent (near Bromley) and at the Guildhall School of Music on Saturdays.
Sorry for the essay but you hit upon my specialist subject!
I do hope the above is helpful and please get in touch if I can be of any further help. Both Kodály and Dalcroze are wonderful ways of developing the musical potential that we all have. They are creative and deeply rewarding ways to teach. You never stop learning how to teach better and the benefits for you and your students are endless.
ENJOY!!!