I'm not sure if I'm doing something wrong but on the page you posted a link to I can add items from either part of the page. I'm including a screen shot of the cart after I add the items.
As for the leashes you may want to set it up just like you have for the toys page but also have the sizes.
If you have not come up with a solution for either I think the best thing to do would be to create a separate table for the sizes and one for the colors. If you have items that will only have specific colors and sizes then you should make a joining table that has a column to hold the id of the item and the id of the size or color. You should have one of these for each table, size and color. Please post back with any more info on any part of this or if you just have some questions.