I must admit I was tempted by the idea of publishing an ebook right away. Commission a cover and internal art, edit and polish the text and then make the work available to all and sundry via the magic of Amazon, Smashwords and my own website. I've already published a number of short stories this way, and my ebook-generating scripts could be rejigged in a matter of minutes.
If this were an adult series I wouldn't have hesitated: you'd be able to buy & download the ebook right now. Unfortunately I don't think the market for kids ebooks is there yet - lack of dedicated readers in kids' hands, most kids books seem to be bought as gifts, etc, etc.
Therefore I have two queries for my junior Hal Spacejock novel out at the moment, and one submission. Each of these Australian publishers specify a 3-4 month response time, and I'm not expecting any favours just because I've been published before.
If I haven't heard anything positive by the first week in September I'm going to prepare the ebook edition of Hal Spacejock Jnr book one. If nothing else I'll be able to put that one out of my mind and move on to book two.
(Cue overwhelming sense of deja vu. A decade ago I went through the exact same process with the adult Hal Spacejock series, only back then we didn't have dedicated ebook readers. I put out an ebook version first, followed by a POD edition, and there were three books in the series available before I finally scored a publishing deal in 2004.)