My dd4.5 is 38" and 28lbs. She is considered underweight. She has some gluten issues. She is on a limited gluten (wheat protein) diet. She also had lactose issues, but is outgrowing both. Your "bigger" twin does not appear overweight to me. My ped said that as long as she is "plotting" along on the chart, meaning that she is following her own curve no matter how far below "normal", she is fine.
On both of them though, I would avoid apple juice. It is the worst juice you could drink. It has a lot of sorbitol which can cause diarrhea and slow weight gain, but can also be responsible for the gain of too much weight in some kids. Depends on the kid. Stay away from juicy juice. It says 100% juice, but it is all APPLE juice, with other flavors added. I use Welch's grape juice instead or Ocean Spray cranberry mixes. I do allow the cranapple. I also buy strawberry banana juice in the cold juice section.
Visit
www.askdrsears.com . He has a whole section dedicated to nutrition along with menus you can print. The information he has on his site has proven indespensable to me. He goes into all of the fruits and juices.
Also, stick to 100% whole wheat. Many bread that say whole wheat are not 100%. Look for the 100%. That is all we buy. As young as they are they will adapt quickly. I only started this a few years ago.
The fruit and veggie tray ideas are great. You can put yogurt out to dip it in as well.
Avoid the artificial sweeteners. These are not good for you. Try to stick with natural and organic. Organic is getting much easier to find and the price is going down.
Now, I know I am rambling, but my last bit of advice is to not worry. Do not put your little girl on a "diet". Just put out healthier choices. Do NOT limit her food, just limit the junk. She NEEDS a certain amt of fat and calories for proper development.
OK, I am done. Sorry for the rambling. I hope at least something makes sense and helps.