No will

[Tinac]

My sons dad passed away, after we split he went on to have 2 more children which he brought up.
He did not marry and was not in a relationship when he died.
does my son have the same claim to the estate as his other 2 children as there was no will.

[PallasAthena]

I assume your son's dad lived in England and his assets are in England.

From what you have said his estate will be shared equally between the three children, one third each.

Under the rules of intestacy (no will) it is irrelevant that they have different mothers or who brought them up. If he was the natural (biological) father of all three then they all have equal rights to inherit.

They also all have equal rights to apply to the probate office to be appointed Administrator of their father's estate.

https://www.gov.uk/inherits-someone-dies-without-will