have you googled toy box plans? I have found lots of woodworking plans online that way.
I even have my students look for plans online then have them modify them to make their own projects.
How you build a toy box will really depend on what tools you have available and what experience you have with them.
Boxes can be as simple as 5 pieces of plywood screwed together with another piece for a lid. not the prettiest of boxes, but it will hold stuff.
using more hardwood and less plywood, and making different types of joints will make your project better. You can also create a build style that matches other furniture in your house if you want.
most toy boxes don't require a scroll saw. If you want to do some decorative scrolling you can glue your pieces onto the front/lid of the toy box. names are an easy place to start with decorations, and won't go out of style. If you cover the thing in baseballs stuff you are almost asking for the kid to start playing football tomorrow, lol. If it is to both kids I would probably just use a last name, that way as they grow up it could sit in either room and not be aquward.