Hello!
I understand the difficulties involved in the balancing act involved in doing all that you can for your children.
I used to take a few approaches: While holding my infant, I picked simple, colorful books to read to my toddler and pointed out the bright colors and shapes to my infant. I also got some large piece puzzles or even coloring books that my toddler could do, and I could help her with, while giving my infant attention. It got my toddler used to independent play, while still getting attention and involvment from me.
You may also want to consider hiring a babysitter one or two days a week for a couple of hours so that you and your children can plan and look forward to "special time" that is set aside for them. It gives them something to look forward to and can help with behavior incentives. One day, the sitter could spend time doing active things that you find difficult with a small baby, while you are getting special time with your infant. The next time the sitter comes, you could have them spend time with your infant while getting special time with your toddler.
Also, don't forget about getting adult time for yourself. It helps to get you through the stress involved with balancing it all, so that you feel more relaxed with them.
If you don't have a sitter or don't know how to find one you feel great about - try The Babysitter Tree. You can give them your "wish list" of credentials, review their information, interview anyone you choose, check their backgrounds, references and credentials, and negotiate their pay, hours, and duties. They come to you - so it is very convenient. You can find their information at www.thebabysittertree.com or call ###-###-####.
Have fun and don't worry - you'll find the way that works best for your family!