Looking for healthy and inexpensive protein fillers and/or meal supplement powders to add to homemade smoothies for kids

My kids (5 & 8) are hitting a stage where they've got bigger appetites. During the summer I like to make homemade smoothies to supplement dinner or as a filling snack before bed (we almost always go swimming between dinner and bedtime.)My usual ingredients for smoothies are usually: low fat vanilla yogurt + frozen berries + bananas + other seasonal fruit. I used to add the generic version of Carnation Instant Breakfast, but I can't find them anymore and the name brand is too expensive. What's a good replacement to use that'll be filling but not loaded with crap? via /r/Parenting http://ift.tt/2r4uxly