Who fits a rear child seat on an ordinary bicycle around Tolichowki?

I've done weekend rides for years, and our son, who's one now, gets wildly excited every time he sees the cycle. My partner has agreed to short rides in our lanes once he has a proper seat and helmet. The shops I've tried only want to sell me a new cycle with the seat already fitted. Mine is old but solid and I'd like to keep it. Is there anyone around Tolichowki, Mehdipatnam or Masab Tank who will fit a rear child seat to an existing frame and check it's done properly? Also happy to hear which helmet you found that fits a one year old's head ❤️