My brother and SIL had a baby 6 months ago and are clearly completely in love with her. I love her too. She's adorable.
But prior to them having her, they doted on my children and were a very engaged aunt and uncle. My SIL in particular seems very irritated around them and will ask them to stand back a lot when they're wanting to touch and play with their baby cousin and won't let them play with her toys.
Another issue is their lack of interest now. They haven't made much effort for their birthdays and will update the family group chat with lots of photos of my new and beautiful niece but won't respond to photos of my kids anymore.
I'm hoping it gets better and eventually they start giving them attention again. They aren't naughty children. They're lovely, but can be a bit excitable around their cousin.
How to handle it?