There is a chance that my DS aged 13 won't be at his Dad's this weekend.
We are helping to organise a local event on Saturday evening and children are welcome. We are going out earlyish on Sunday morning so I thought having DS there would be a good excuse for me / DP to leave early. DS could also stay at home on his own as we are literally only down the road anyway. I had no plans to get a babysitter at all.
Now, we are not due to have the DSC this weekend. DP has suggested that DSD aged 15 babysit and we pay her, meaning a 10 mile trip to collect her and drop her off . He says this means he gets to see her for an extra night and it will annoy her Mother. DSD is up for doing this to earn some more money from us. 
So, of course, now when I say DS doesnt' need a babysitter, I will be stopping him from seeing his kids!