I'm in two minds because you're staying at their house, yes FIL should try and be quiet, but kettles can be noisy, so it might have happened anyway. If I was him I'd think oh DS & DIL are here, they'll see to him. I don't think he owes an apology at all, if he wanted a drink it's his house.
Have a word with DH, saying, if possible can you ask FIL to be quieter, DC was up several hours so will be grouchy today.
DH might say we're guests in their house, we can't tell them what to do.
If DH won't have a word, maybe say to MIL, really really sorry to be a pain, but FIL was banging about and woke up DC, who then thought it was playtime. Can you ask FIL if he could be a bit quieter, so shattered from DC's late night antics. I'm really sorry again, I know this is your house.
Hopefully all will be sorted.