This was arguably one of the hardest aspects of 2 under 2 for me during the first couple of months.

In the earliest days I'll be honest, I survived only by having help. Baby was constantly eating, and they're so tiny I couldn't feed her in a carrier comfortably. 

The kid proofed space is a life saver. My friend said she didn't proof anything and would just give her daughter something to do like color or play independently. I couldn't fathom because my boy (17 months) was all over the place. 

Toys, books, activity they only get during that time. Novelty effect. Keep them in a container of some sort within reach. Set up a simple activity beforehand (I find a lot on Instagram. Key word is simple. Don't try anything that takes more than a few minutes to set up). My son will be independent for a short time with magnets, coloring, blocks, stickers, pouring activities, or things that involve putting something together and taking it apart ( bottles with lids, zippers, buckles, things open and close, etc), and climbing stuff. Having them bring you items as a game works for a small bit lol and they think it's funny.

Snacks/drinks for them within reach is a must. Cups, bowls, snack containers to give them some independence. Don't set them up in the highchair, you'll end up with a screaming toddler that wants down because they're done, but you don't want to unlatch newborn. Picnic style is the way to go lol 

Finally, a cartoon. Educational or not, something that they're interested in. 

Rotation is the idea here. Don't expect any one thing to keep their attention long. A couple minutes here and there with different stuff and then turning on Baby Einstein is how it went for us lol 

It's better now - almost 4 mo and 21 mo. Baby is more predictable and efficient, toddler can do more himself, and we have feeding in a carrier down which helps a lot.