DS is 2, he used to regularly be taken out on Thursdays by PILs for a few hours so they could spend some 1-1 grandparent time with him. Then DS2 was born and FIL had an accident which meant that they didn't take DS for about 4 months. We've tried to resume the arrangement now FIL is better but DS is hysterical. He seems not to like them at all. The minute he sees them he gets really, really upset. Clinging to me and crying. Not just a typical toddler 'paddy' but proper sobbing 
They came for him this morning and I made him go. I strapped him into the car seat myself even though he went rigid and tried to stop me. I feel so bad but I don't know what to do. Apparently as soon as they're up the road he is 'fine' - that's what PILs tell me - they say if he continued to be upset they'd bring him back.
What do I do? If I don't send him I will really hurt PILs who adore him, if I do I feel like I'm hurting him. Or am I being pfb?
Btw he goes to nursery 2 days a week and is usually fine on drop off, although he does get a bit tearful now and again - although nothing on a scale with how he is with PILs.