First aid:
I would firstly make sure tommy has enough space and make sure the other children are moved away as they could also get injured. I also need to call for help as someone else should be there to supervise me, or help me. The teacher in charge of the class will also be asked if she has any idea what the chemicals are as they have been kept in an unlabelled bottle.
I would then follow the acronym DRAB
Danger: look around to see if there is any danger around, As the child is sat in a puddle of chemicals there is danger around there fore if the child is able to I would get him to walk away from the puddle into a clear area, however if he is either unable or refusing to move I would have to place obstructions over the chemicals so I could stand on top of them enabling me to get to Tommy.
Response: The best way to get a response is to simply talk to Tommy, however as he is crying it will be difficult for him to communicate with me, Although the fact that he is crying can be seen as a good thing as it shows that he’s not unconscious. If tommy were to be unconscious or unresponsive whilst talking would be to pinch his ear to see if he squirms.
Airways: As Tommy is conscious I will not need to worry too much about airways, as he is able to talk and cry. I also need to try and figure out whether he is likely to be sick as this could block his airways. The best way to do this is to just try and calm him down, or stop him crying so that he can talk to me, the best way of doing this is to tell him everything will be okay and that he is not in trouble for going in the chemical cupboard as he could be crying because he is scared he is going to be told off.
Breathing: Tommy is clearly breathing as he is crying.
I would also be worried for chemical burning as most are irritant to the skin, especially for a 3 year old as his skin will be thin.
It is vital that I remove the chemicals from his skin, and any contaminated clothes. The burns or occurring burns will need to be rinsed and a bandage of some sort will need to be loosely applied. An ambulance will need to be called if there are any signs of shock, for example if Tommy faints, if the burn covers more than 8cm of the skin or the first layer of skin burns through.

Tommy can start to suffer from shock, leading to him being unresponsive and unconscious, if he becomes unresponsive and has a low/no pule CPR will need to be done. CPR on a child is 30 chest compressions at 100-120 per minute, I will then need to open the airways to give two rescue breaths and continue to repeat this. I would also need to follow the acronym SAMPLE:
S: signs and symptoms- Signs are what you can see and symptoms are what you can report.
A: Allergies- Tommy could be allergic to something with in the chemicals, or the medication that the doctors will need to give them to get the chemicals out of his system.
M: medication- Tommy may need medication to get the chemicals out of his body, they could be burning and deteriorating his insides if he has swallowed any of it.
P: pertinent medical history- Relevant medical history, the best way to do this would be to call Tommys parent/guardian and ask for anything else that could be causing this to happen.
L: last oral intake- It will be important to know what Tommy has eaten as you will need to know if he is likely to sick anything up likely to block his airways.
E: events leading to the illness or injury- it will be difficult in this situation for Tommy as we will not know how he got into the cupboard and how the catch broke, however if we do find out it could help towards finding out what chemicals he may or may not have swallowed.

Whilst I am dealing with Tommy I would make sure another member of staff clears a cupboard with a lock on to put all of the chemicals away in, however any chemical being kept in a label less bottle will need to be thrown out, in the correct way, this would be to get in an expert team to come in and find out what they are and how to throw them away.