That's heart breaking, DS2 is 4.5, he loves fireman sam, has a fireman sam lunchbox, wears his fireman sam clothes on non-uniform day etc, he has stabilisers on his bike and a 3 wheel scooter. He too has speech problems and does seem a lot younger than some of the Ben 10 boys in his class, but they are nearly a full year older than him.
DS1 (he's 8 now) still used to love thomas when he was that age, although if I'm honest there did come a point when peer pressure kicked in a bit and he still played with his thomas toys at home all the time but did move away from thomas clothes, lunchbox etc. but I think that was in year 1 and certainly wasn't due to any actual bullying.
When DS1 was in reception/year 1 the school actually banned anything ben 10/transformers/power rangers and asked us not to let them watch these programmes at home as they were having trouble with scenes being replayed in the playground.
I am stunned at the 7/8 year old child punching him in the face, none of DS1's, he's 8, classmates would do that, they really wouldn't.
This isn't normal, it isn't, what a terrible introduction to school for him, please don't think this is his, or your, or Thomas's fault, it's not, school need to come down on this fast.
Oh and by the way, DS1 8, still watches Thomas in the morning before school and plays with the thomas trains sometimes and all of mine love Peppa Pig, 8 year old included, as mary said, they just keep quiet about it.