Restrictions of Play Store on custom ROMs Please could someone correct my understanding? I read that once a phone has a custom ROM loaded, the play store can not be used on it again. However after more reading I'm not sure if this is the case?

I'm sure the answer is complicated so to simplify it, all I want to do is convert an old phone (HTC wildfire) into a dedicated device for my toddler that will just be used for offline games.

I don't need to remove features as he will be supervised, but I don't mind if the barest of ROMs is loaded as long as I can load games from the play store: I just want to speed the phone up, as at the moment it is awfully slow. (I have already tried restoring to factory settings and installing updates.) 

Help would be appreciated!
There is no such restriction. I use custom ROMs on two of my devices, and the Playstore is acting normal.

The only problem you might face is that the Google Play App won't come pre-installed. You need to flash a package called "GApps", which must match the Android version used by your custom ROM. Usually, the corresponding links are pointed out on the page where you download your ROM from.