The volume will really depend on the channels you use to sell it (and how it is being sold on those channels). There are a few different approaches I'd recommend:
a) take preorders (most ecommerce solutions have preorder solutions built in and, in true valley style, there's a startup that only does that -- https://www.trycelery.com/ -- if you have woocommerce or shopify, don't know that celery offers much extra in its preorder solution but check it out)
b) kickstarter volume can probably be extrapolated into broader market potential -- ask some folks who've gone that route to see if there's a correlation/formula you can use to gauge market volume from kickstart demand
c) approach the toy buyers at a couple of retailers you'd want to work with (esp. TRU and AMZN). see if they'll take a call although you may not be far enough on. they have their finger on the pulse of the market.
d) to complement c, approach some toy distributors or 3pl's that focus on toys -- the woot team was a toy/electronics distributor before woot was born, i think etoys still does it and there are other toy distis out there who may give you some market guidance.
e) look at comparable products on the channels you want to sell on. (NOTE -- there's a significant difference between amzn selling your product and being a 3rd party seller on amazon so caution with this.) from the number of reviews and popularity of those products, you can probably gauge a decent sense of the market (there's usually some current research out there pegging the number of reviews on amzn to order volume),
i can't underscore enough how you build your channel will impact margin and volume. selling wholesale will give you volume and some early market validation but radically alters the margins. also, you'll need to manage your reseller channel or have someone do it for you. selling direct means you now have to figure out marketing+fulfillment+cs as well as everything else but your product margins are better (net margins might blow if marketing and fulfillment are more expensive than you anticipated). doing both is possible but you'll probably end up not being particularly strong at either.