No it is not. Unless you are a big name you place yourself next to strong competitors that are supported by big budgets. Start small with friends, friends of friends, get reviwes, create a blog become known and maybe spend some money with FB ads. If you have the budget print some copies and fight for your space with readers clubs etc. It is a tough business with a lot of competition and therefore you must work in order to be noticed .
It can be, if you niche down. Generally, you are going to spend a lot if you target keywords like "Halloween Book," but if your book is specifically about a kid who is making a Jack O Lantern, target some things like "Jack O Lantern Book." Of course, you won't get the volume, but you will get a better conversion rate. Through the last 6 months of Amazon ads I have sold over $1MM that can be attributed to ad clicks and have spent less than $30k.
Its TOUGH. I marketed a childrens book a long, long time ago when their advertising was less evolved.
My suggestions: Locate top mommy bloggers and pitch 'how to' related content for your book. Offer guest blogging and pitch 10- ideas for that given blogger. All it takes is one YES for you to have a flood of targeted , referral traffic. I can share how this is done if you would like