I've just got permission again from my Ex to start having my 2 girls again on Weekends and would love any advice from people of the do's and don'ts with a 7 and 5 year olds
No matter what the reason for the breakup don't ever talk trash about their mum. The kids have a right to love and trust both of you freely and without fear and apportioning blame would get in the way of that.
be a fun loving dad, have boundaries, use discipline when needed, be kind, thoughtful, caring, play with them, hug them, make them nutritious meals. Be a good role model and you'll be fine.