A gift certificate for babysitting for the parents. The kids don't need anything.

How about getting each a US Savings Bond of some type?

Books, either age appropriate board books, or story books, or children's classics from the Everyman Library.

https://www.penguinrandomhouse.com/series/HCS/everymans-library-childrens-classics-series

Mommy/daddy and me swimming lessons are good too. Along with suits and towels if you'd like.

Our granddaughter just turned one last Sunday. Per a suggestion from our daughter, I ordered this water table. Big hit and our daughter loves that it's an outside activity. I know you're buying for twins, but maybe they could share one of these...?

Do you know if they already have activity walkers? They're especially nice when babies are taking first steps but still great beyond that. Our grandson continued to play with his long after he started walking. Luckily it's still in great shape for our granddaughter now.

Books, Baby doll, truck and then clothes that are always needed. Also diapers or gift cards.

Ask the parents.

I’m with sushipup. With one year old twins it’s the parents who need a gift. How about taking the babies for a full day of fun and sending the parents off for a day out with a picnic or nice meal booked?

Fat Brain toys has the very best of toys for children.

Books are never wrong. Anything interactive, creative, outdoor play. Without knowing the parents or living situation it's tough to suggest anything at that price tag. I too would suggest a modest gift and something for the future like a savings bond.

Get something consumable. My kids had way too many toys. Most were given as presents for them. I like the zoo idea for them. Other place visits depending upon what is local would be fun too.

Do you have any idea how big these kids are? I would buy them coordinating outfits in 18-24 month sizes. It could be play clothes or something suitable for pictures.

This isn't consumable, but it's not as intrusive because it is outdoors. My kids enjoyed outdoor decorations like the pinwheels and thing that spun in the wind. Or you could get them some fun little animal statues like frogs or turtle.

The difficulty with the savings bonds is that the person the bond is registered under must also provide a SSN. Depending on how close to the parents the gift giver is some parents will not provide their children's SSN. If registered without the child's SSN whoever's name is on the bond could cash it then the child would later have nothing. If the person did hold it until later for the child the money depending on the laws at that time may be considered a taxable gift.

I agree to give something that is not another plastic toy or stuffed doll or animal! Most kids have a mountain of them by that age and there are more to come in the coming years. Give the gift of an experience, for sure.

what is your relationship to the twins? if it is far removed, the family takes care of their needs/wants....

if the parents opened a 529 savings plan for college, give toward that. i do for my niece's children. she gave me their "number" and i gift on-line. So easy!

if not, donate to their savings account, if they opened one

i agree, one year olds don't need toys etc...

My son had one of these wooden activity cubes when he was that age. It was small enough to go in my car when we met up with other parent/toddlers at the park and could keep multiple little ones engaged for quite awhile. My son also used it to pull himself up, when he was transitioning from crawling to standing and then walking. https://smile.amazon.com/Battat-Wooden-Activity-Discover-Animals/dp/B07BF1V8K8/ref=sr_1_1?dchild=1&keywords=toddlers+play+cube&qid=1624115374&sr=8-1

I also had an electric bubble making machine that I remember being quite a hit for backyard fun. https://smile.amazon.com/Professional-Upgraded-Portable-Automatic-Christmas/dp/B088STZW8Z/ref=sr_1_7?dchild=1&keywords=bubble+machine&qid=1624115802&sr=8-7 

I don't think 1 year olds need expensive toys but, but they do learn from play. The right toys can be good for them and give the parents a short break.

For years I've given sets of these to kids whose families would appreciate them, use them and remember they have them. Perhaps with covid, the days of blowing out candles will be over, however.

Birthday cake candle holders

The numbered ones would work great on the birthday child's cupcake and can be used for their whole lives except the double digit years (22, 33, etc):

candle holders

I found some cute pool things along with a gift card. The family spends a lot of time at the pool. They know babysittiing is always an open offer