I usually do it with a dry iron just like Steam A Seam.

If it's a fusible interfacing, then I use a damp cloth and/or steam.

If you can remember the brand, check their website as the instructions vary from type and mfr.
I hate it when I forget how I did something when I get back to working on the project!
Cute idea for a kid's quilt.

i have no idea what the brand is. The sales slip that I had when I purchased it is gone. I bought it at Fabricland in Ontario when I was there visiting family and there wasn't any instructions with it.

I found this blog entry regarding fusible interfacing.

I have always used a dry iron at as high a heat as the fabric can take but in the blog she uses steam and a damp press cloth.

http://www.pinkchalkstudio.com/blog/2008/10/27/fusible-interfacing/

Thanks Ladies. I tried using steam from my iron and then ironed it on. I washed one piece and dried it in the dryer and it was fine.