Son and step son

[Nic2300]

My son and step son are very friendly and my son with my ex keeps asking can the step son go up to his mummy’s house (my ex). I’ve told him that they spend enough time with eachother and when there with their mummy that’s her time to spend. Not sure if I’ve said the right thing as they are only kids

That's wonderful that they get on so well. That must be amazing.
Depends on what your ex says... She may see it as it our son's friend coming over. She may see it as her ex's new step son who she wants not to see. Has he spoken to his mum?
Your not in the wrong or right either way.