Do not call literary agents or publishers. All the information you need is on their websites, and you'll mark yourself as an amateur if you call.
There's a similar thread with more replies: www.mumsnet.com/Talk/am_i_being_unreasonable/3108430-To-ask-about-publishing-firms As I (and others) said there, self-publishing a children's book, especially a picture book, is pointless. You won't sell more than a handful of copies, if any.
Anyway, on to your question! How many agents have you queried? If you queried 50 and none of them are interested then it's a fair assumption that they don't think your manuscript is publishable. Bear in mind that doesn't mean it's crap: not publishable can mean anything from it's crap to it's the wrong length to it's fine but not unique enough to sell in a competitive market.
If you've sent it to five agents, then you can't read anything into silence.
And how long has it been? I queried mostly US agents, but the UK agents took much longer to respond on average. Believe it or not, I had a reply a full 17 months after I'd sent a query. She did apologise for the delay. :grin: The length of response has no bearing on the outcome, either. I had a rejection from one agent 13 minutes after querying. I had a full request from another an hour after sending. I had a full request after eight months, long after I'd signed with my agent. The one that took 17 months was a rejection.
I queried around 50 agents. 15 of them requested the full after reading my query and sample pages, and I signed with an agent within six weeks of sending my first query. My manuscript obviously isn't total crap, or it wouldn't have got that response, but 35ish still rejected me. Nobody, and I mean nobody, gets a 100% request rate if they query more than a couple of agents. It's so incredibly subjective.
Now picture books are different - you send the full text with the query so, unlike novelists, you can't gauge how good your query and sample is from how many full requests you get. But I would still keep trying. I know authors who queried the usual 30-60 agents and only had one request, but that one offered representation and sold their manuscript. It only takes one.
Just please don't be sucked in by a vanity publisher, or "assisted" self-publishing. I know you didn't give any hint that you would, but so many authors are exploited.