Tailtwister & Pizzahutlover:
Not sure if the DCs involved are only children or just PFB - but I think your emotion is a recognition that starting primary school is a real 'right of passage' - it marks the end of them being your little baby and the beginning of them being a 'big boy' or 'big girl'.
Now in the big picture - if you were to ask yourself what do you want for this little newborn babe in your arm - it would of course be to grow up and be happy and successful. Part of that process is schooling.
Primary school really isn't the end of your DS being the centre of your world - why that can go on until they're well into their 20s (and no doubt invovle you footing many a bill - as my S-I-L will confirm) - but it does mean that they're starting to make their way in the world.
Primary school is a safe, secure environment to make first friendships, learn new skills (including social skills) and start to discover what you might be good at.
My advice to you is if you feel strongly you want to be involved - then don't be bashful, get involved.
-volunteer to help on fieldtrips
-volutneer to help at PTA activities
-come to reading mornings or special activities
-attend assemblies
-arrange play dates
-get involved with the school (many ask for volunteers to read with children)
-Consider becoming a parent governor
Your relationship with your child will change - they'll develop their own personality, likes/ dislikes and querks. But they'll also grow to be a close friend, confidant and playmate - which is a whole new wonderful world for both of you to explore and a fully two-sided relationship.
Primary is a lovely time and you'll still have your little boy or girl to dote on - but you can enjoy their discoveries, you can fire up their interest in subjects (visit a museum, watch a documentary, visit a forest, visit a RSPB bird reserve, see a film, etc...) and you can help them grow into that man or woman you envisioned when you first looked down on your newborn. There's fun to be had in sorting out a costume for a superhero at last minute or decorating an easter egg for a competition. You will have good times in primary - honest!
It's a tough time on us Mums and Dads, when little ones start school. Four can seem very young and it is a shock to see how big Year 6 kids can be. There's no getting around it. But there will be good times to come - school plays, assemblies where your DC gets an award, gossip about a great day at school, exciting discoveries, etc...
It's natural to shed a few tears now, but remember it isn't all bad, starting primary has to happen sooner or later. So try (although it may be an effort at first) to look on the bright side, to enjoy big events like first day at school, first field trip, getting chosen to be on student council or team leader, etc... becuase it can be a lot of fun for you too!
HTH