Do Chillkids make a charge? This is not clear from their website.
I agree that it can be helpful to see what you have been submitted for and, if you don't act full time, it can be helpful to choose which jobs you are submitted for. In my experience this is not how it usually works though, and I think there are good reasons for this:
Jobs can come up at very short notice and require very fast response times (especially commercials). If an agent has to check to see who is available, this will lead to delays. From the agent's point of view it is simpler to know in advance when a client is
not available - then they will not submit the client for a job they couldn't do. Most agents will talk to their clients when they take them on and discuss what sort of jobs they might be suitable for.
If Chillikids are leaving it to clients to decide whether or not they are submitted, this
suggests to me (though of course I don't know) that they a) have a very large number on their books and b)submit more than one client for each job. Both these possibilities would provide an explanation as to why many people on their books don't get called in for castings.
If you want to act, I would maintain it is a good idea to seek out an agent specialising in this area that makes no charge. The reason for this seems to me to obvious: if the only way an agent makes money from you being on their books is for you to get work, they have a much greater incentive to work very hard indeed to get you
seen for work! If you are paying them to be on their books, the easiest way for them to make money is to encourage more and more people to sign up (because work is hard to come by) - this, of course, dilutes the amount of work they can do to promote any one individual client. In my opinion, this way of working means that the agent wins every time they take on a new client and all their clients lose a little.
If you can't get on to the books of an acting agency that makes no charge, it is only at this point that I think you could consider alternatives. It is certainly true that Casting Directors will take applications more seriously from certain agents - but this does depend a lot on what sort of relationship the agency has with the CD. Sometimes, quite small agencies have good relationships with particular CDs and directors.
In acting terms, it is NOT usual for an agent to submit several clients for the SAME role. Most acting agencies will limit the numbers of people in the same casting bracket for precisely this reason. Obviously for commercials this can be different as CDs often see large numbers of people.
In my opinion (always ready to give that

): if you want acting jobs, it is much better to be with an agency that insists on auditioning children or seeing adults in shows/showreels. This is because a CD will, over time, trust this agent to submit only those children/adults that have the requisite looks/skills/experience and will take submissions from this agent seriously.
It's also always worth keeping in mind that, however nice the agent is, he/she is in the business to make money. They are unlikely to spend much time worrying about or seeking out unpaid "experience" and may not have time to devote to you as an individual unless you are "hot property".
Finally though, I would refer people to Golightly's post:
http://www.notapushymum.com/phpbb/viewt ... =8&t=14145
An agent that is the right one for one person won't always be the right one for somebody else.