This is not a LCC/charter issue. Just try LGWMCO on BA using free check in and seat selection 24 hours left. There is usually a couple of twos and ones and that's it. Everyone paid (a lot more than TCX too) to get seats together or had status. Whether you pay or have status it's costing you a lot of money either way.
Depending on airline policy the cabin crew may intervene if the seating arrangements contradict their ops manual or cabin services manual but don't necessarily have to do any it's just because someone doesn't get their first choice. As with everything first come first served but the problem seems to be resolved anyway.
No I'm not in customer services. I sit behind a bullet proof door locked safely away from it all :-). And sorry for the attitude but many people use their kids as bargaining chips and that doesn't sit well with me.
If I want something for my kids, or I feel there is no one to look after them, or to take care of them in the unlikely event of something go wrong, or if I feel they may be at all distressed then I'll pay. If you've paid £3500 for a flight then he allocated seating fee is a drop in the ocean.