A professor of human performance says children can reverse negative health impacts associated with lockdown within three months of being regularly active.
It comes as underage non-contact outdoor training in pods of 15 people or fewer can restart from Monday, as coronavirus restrictions are eased further.
Professor Niall Moyna is from the School of Health and Human Performance at Dublin City University (DCU).
He told Newstalk Breakfast: "There are a lot of very, very happy parents in Ireland today.
"If this lockdown has taught us one lesson, it is the importance of sport to our society - not just the elite sport, but sport at the grassroots level.
"And the importance that that plays in the development of children and adolescents.
"There isn't a 'one size fits all' here, there are kids living in inner-city apartments and there are kids living in rural areas - maybe three miles from their neighbours - and haven't had the opportunity to interact with them now since Christmas.
"So I just think it's a great day."
Citing a 2019 German study, he said: "Between the ages of three and six, that's when most kids will put on excess weight.
"And if you're overweight as a three-year-old, you are 90% likely to be overweight as a 15 and 18-year-old.
"So that's the issue - but the good news is that children are extremely malleable, and... if there are any negative impacts on their overall health - whether it's through weight or loss of fitness etc - I think that can be addressed within three months of being regularly active again".
And Prof Moyna said physical interaction is very important for younger children.
"We all know the health benefits - and God knows what we're going to find out in the next six months in relation to the health and the impact that has had on health - but we know that sport is brilliant for developing self-confidence and self-esteem in children.
"I think what parents will find out most, and they'll find the quickest, [is] the impact it's going to have on their mental health.
"Just being around your team mates in a fun environment is going to be absolutely tremendous".
And he said he hopes the lockdown will not have too big an impact in the medium-term.
"I don't want to be alarmist, hopefully it won't be that bad.
"But most of our health behaviours are adopted in childhood that we take with us for the rest of our life."