I had a "boyfriend" briefly at 12, we only ever spent time with each other either in school or at each others' houses (with parents in attendance!) where we had the odd rather chaste kiss and played a lot of subbuteo. Did used to find it odd that his mum popped in to his bedroom every ten minutes to offer me a cup of tea, but just thought it was because she was Scottish 
My mum and dad took the whole thing very seriously (to my face, I am sure they were pissing themselves behind my back) and included him on family days out etc. It was lovely, I got bored after a few months and that was that until I was 15/16 when the real fun began.
I think you should do the same - demonstrate great interest in him, invite him for dinner, to the museum, to the cinema etc - all with you there too. Then you will be able to gauge fairly quickly what the situation is. If (worst case scenario but possible) he is after a younger, easily manipulable girl to have sex with, he will move on fast. If (far more likely) he is a decent nice boy, he will come along, go bright red a lot, possibly hold hands behind your back, no harm done.
You do also need to talk to her about contraception etc. Don't rely on school sex ed - my friends twelve year old son asked her last week if it was legal for him to buy condoms before he was 16 - clearly with all the banana-related excitement in the class some key messages about consent and contraception had got transposed!