I'm probably less anti-LTN than others here (as it's my local airport, and I used to work on the airport site), but you have to know its vagaries to get on with it. I've always found security pretty friendly and efficient there. Departures is pretty poor - you won't get a gate until 20-odd minutes before, so there'll be starting blocks by the Pret, and an undignified scrum to airport-speed-walk to the gate (especially if you're on Ryanair, using the distant "roundhouse" gates where they make you queue up outside, no matter the weather). The rest of the departures area resembles an unloved motorway services, so I usually just find myself a table in Pret (if quiet) or Wasabi, as I quite like their mochi. Book priority boarding, then you can avoid the scrum to the gates, and the eternal queue actually at the gate, it's just a bit more relaxed. Arrivals are OK - never had a serious queue at immigration there (again, this is pre-rona/brexit) and there's an M&S Simply Food to get your tea and a pint of milk on the way home.

Gatwick, though... Again, last time I was there (North Terminal, U2 to NCE), I thought it was excellent - particularly through the eyes of someone travelling with a small child. Lots of well located family parking (though half of it was occupied by taxi drivers), the easyJet bag drop was huge and very well run, even with a relatively complex check-in, there was a dedicated family security area which was fast and friendly, and the baby-changing toilets were right there are you got in. Little play area too. However, Gatwick always changes character in the summer holidays!

But yes, personally, I'd take the train at the moment. Schiphol sounds painful too! I'm just hoping my midweek, midday U2 flight from LGW to Italy in August isn't too awful (and does actually go ahead...)