Deficiency of Vitamins B2 and E can lead to neurological disease in chicks.
These deficiencies can be treated if caught early enough. I would add a vitamin supplement to their water.
What have they been fed on, a modern chick crumb diet, that is fresh should have enough added vitamins.
Other conditions that can cause paralysis are:
Marek's Disease - This is caused by a herpes virus and can lead to progressive paralysis, some birds will recover, but they remain carriers of the virus for life.
Epidemic tremor - another viral disease. There is no cure.
Newcastle Disease - can cause paralysis, but this is a notifiable disease in the UK. The last outbreak in chickens was in 1997
If Tom is panting then he may also have a respiratory problem. Although a lot of respiratory infections are caused by viruses, poultry often benefit from a course of antibiotic as they are prone to secondary infection.
I think Tom would really benefit from a trip to your vets where he can be examined and appropriate treatment started immediately.
He is going to need a lot of nursing care. He would benefit from being propped up in an upright position, with some soft towels. Make sure that he has easy access to drinking water and can get to his feed. Add in a vitamin supplement. He would also benefit from having some live yoghurt or probiotics added to his feed.
Please reply if you have further questions
At 3 months, they should be onto a growers pellet, this does contain slightly less protein, as the chicks demand for protein decreases as they age (24% protein in starter diet, 20% in growers diet). When they reach around 16 to 17 weeks those that are to be kept as laying hens should be switched to a layers diet.
If they grow too fast, some of the heavy breeds can get leg problems, as they are too heavy.
At 3 months he could well be beginning to crow. They start to crow as they reach maturity and this can vary greatly between the different birds and also the time of year also effects how quickly they mature. Crowing is often spasmodic at first and their first few attempts often sound like they're being strangled!
It may be nutritional, there could also be a genetic aspect.
As I listed earlier there are also viruses that can cause neurological problems.
With nutritional deficits, if they are tackled quickly then recovery can be complete. The longer they have the deficiency, the more likelihood there will be permanent damage.
I would restrict their exercise for the time being, until they seem stronger, to reduce any joint damage.
If they are not improving or there is a deterioration, then a trip to your vets would be a good idea.