How likely is it that DC2 is also on the autism spectrum?

[jigglejiggle2]

DC1 was a late walker and talker - diagnosed with ASD at 3 years old.

DC2 was a late walker and talker too but now at 3 years old seems miles ahead of DC1 with talking, understanding, and social skills in general, and currently shows no concerns to nursery staff, or indeed us, but is it possible it could present later or be more subtle?

Yes it's possible. Never had concerns about my own child until he was around 6.
I know of several children, especially girls, who haven't really become obvious until pre-teen age.
Some people are only diagnosed as adults.

Ds showed no obvious signs until 11. Dd at about 15!

girl or boy?
Are you or your partner also on the autism spectrum?
It's quite possible to be honest, but if they are, it could be in a really different way to your eldest.

DC1 is a boy, DC2 is a girl.

We think we can see it in ourselves and wider family, but no formal diagnosis among any of us.

possible but seems like you're clutching at straws for it

its possible, girls do present differently to boys. I have two daughters with autism - they’re both very different to each other.

They generally reached their milestones on time - although one needed speech therapy when she was about four and the other couldn’t be potty trained.

Extremely likely especially given the genders, girls present differently - please consider this x

Just wondering if it's possible for two people to have the very similar developmental trajectory for the first two years of life (eg late walking, talking etc) but then at 3 years old where one was diagnosed with ASD, the other is seemingly NT.

they're siblings so naturally will have things in common. doesn't mean its a brain thing

I don't know, children are all different. All of mine were late talkers but early walkers, one autistic and the others not.

Honestly OP it could go either way. Sounds like she's probably NT but not definitely. Just a case of watch and wait.

Ds we knew was autistic before 2. Dd is the second born, she was a late talker (almost four before she spoke) we thought she wasn't autistic then started school in the second year it became obvious she was she's just very different from her brother and learned to mask things.